Cathode active materials for lithium-ion batteries

ABSTRACT

Compounds, powders, and cathode active materials that can be used in lithium ion batteries are described herein. Methods of making such compounds, powders, and cathode active materials are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 62/307,956, entitled “Surface-Modified Cathode Active Materials for Lithium-Ion Batteries,” filed on Mar. 14, 2016, and U.S. Patent Application Ser. No. 62/307,964, entitled “Cathode Active Materials for Lithium-Ion Batteries,” filed on Mar. 14, 2016. The content of each application is incorporated herein by reference in its entirety.

U.S. GOVERNMENT LICENSE RIGHTS

This invention was made with U.S. government support under WFO Proposal No. 85F59. This invention was made under a CRADA 1500801 between Apple Inc. and Argonne National Laboratory operated for the United States Department of Energy. The U.S. government has certain rights in the invention.

FIELD

This disclosure relates generally to batteries, and more particularly, to cathode active materials for lithium-ion batteries.

BACKGROUND

A commonly used type of rechargeable battery is a lithium battery, such as a lithium-ion or lithium-polymer battery. As battery-powered devices become increasingly small and more powerful, batteries powering these devices need to store more energy in a smaller volume. Consequently, use of battery-powered devices may be facilitated by mechanisms for improving the volumetric energy densities of batteries in the devices.

Lithium transition metal oxides can be used in cathode active materials for lithium-ion batteries. These compounds can include lithium cobalt oxide or derivatives thereof. These compounds can be in the form of powders.

SUMMARY

In a first aspect, the disclosure is directed to a compound according to Formula (III):

Li_(α)Co_(1-x)M_(x)Al_(γ)O_(δ)  (III)

wherein M is B, Na, Mn, Ni, Mg, Ti, Ca, V, Cr, Fe, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru or a combination thereof, 0.95≦α≦1.10, 0<x<0.50, 0≦γ≦0.05, and 1.95≦δ≦2.60.

In some aspects, M is Mn, Ni, or a combination thereof, 0.95≦α≦1.10, 0<x<0.50, 0≦γ≦0.05, and 1.95≦δ≦2.60.

In another aspect, the disclosure is directed to a powder comprising particles. The particles include the compound according to Formula (III).

In another aspect, the disclosure is directed to a powder comprising particles that have a core and a coating. The coating is disposed over at least a portion of the core. The core includes a compound selected from the compound of Formula (I), Formula (IIa), Formula (IIb), and Formula (III):

Li_(α)MO_(δ)  (I)

(x)[Li₂M¹O₃].(1-x)[LiM²O₂]  (IIa)

(x)[Li₂M¹O₃].(1-x)[Li_(1-y)M²O₂]  (IIb)

Li_(α)Co_(1-x)M_(x)Al_(γ)O_(δ)  (III)

wherein, when the compound is Formula (I),

M is selected from Co, Mn, Ni, and a combination thereof,

0.95≦α≦2, and

1.95≦δ≦3;

when the compound is Formula (IIa),

0≦x≦1,

M¹ is selected from Ti, Mn, Zr, Mo, Ru and a combination thereof, and

M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru and a combination thereof;

when the compound is Formula (IIb),

0≦x≦1,

0≦y≦1,

M¹ is selected from Ti, Mn, Zr, Mo, Ru and a combination thereof, and

M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru and a combination thereof; and

when the compound is Formula (III),

0.95≦α≦1.10,

M is selected from B, Na, Mn, Ni, Mg, Ti, Ca, V, Cr, Fe, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru and a combination thereof,

0≦x≦0.50,

0≦γ≦0.05, and

1.95≦δ≦2.60.

In some aspects, the compound is Formula (I),

M is selected from Co, Mn, Ni, and a combination thereof, 1≦α≦2, and 2≦δ≦3.

In some aspects, the compound is Formula (IL),

0≦x≦1, M¹ is selected from Ti, Mn, Zr, Mo, Ru and a combination thereof, and M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru and a combination thereof.

In some aspects, the compound is Formula (IL), and 0<x≦0.10.

In some aspects, the compound is Formula (IIb),

0≦x≦1,

0≦y≦1,

M¹ is selected from Ti, Mn, Zr, Mo, Ru and a combination thereof, and

M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru and a combination thereof.

In some aspects, the compound is Formula (IIb), and 0<x≦0.10.

In some aspects, the compound is Formula (III),

0.95≦α≦1.10,

M is selected from Mn, Ni, and a combination thereof,

0<x<0.50,

0≦γ≦0.05, and

1.95≦δ≦2.60.

The coating comprises an oxide material, a fluoride material, or a combination thereof.

In some aspects, the core includes a compound according to Formula (IIa). In some aspects, the core includes a compound according to Formula (IIb).

In some aspects, the core comprises a compound according to Formula (III). In further variations, 0.001≦γ≦0.03.

In one aspect, the disclosure is directed to a compound represented by Formula (IV):

Li_(α)Co_(1-x)Mn_(x)O_(δ)  (IV)

in which 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20.

In a further aspect, 0<x≦0.10.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.98≦α≦1.01.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 1.00≦α≦1.05. In a further aspect, 0≦x≦0.10.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.95≦α≦1.05 and 0.02≦x≦0.05.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 1.01≦α≦1.05 and 0.02≦x≦0.05.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.95≦α≦1.05 and x=0.04.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 1.01≦α≦1.05 and x=0.04.

In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.98≦α≦1.01 and x=0.03.

In a further aspects the compound has the structure of Formula (Va) or Formula (Vb):

(x)[Li₂MnO₃].(1-x)[LiCoO₂]  (Va)

(x)[Li₂MnO₃].(1-x)[Li_((1-y))Co_((1-y))Mn_(y)O₂]  (Vb)

wherein 0≦x≦0.10, and optionally 0≦y≦0.10. In some variations, 0<y≦0.10.

In some aspects, the disclosure is directed to a powder comprising particles, the particles comprising the compound represented by Formula (IV): Li_(α)Co_(1-x)Mn_(x)O_(δ). In various aspects, 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20. In various aspects, 0.95≦α≦1.10, 0<x≦0.10, and 1.90≦δ≦2.20. In some embodiments, at least a portion of the particles have a smooth surface. In various instances of these embodiments, at least a portion of the particles have a tap density equal to or greater than 2.2 g/cm³. In various instances of these embodiments, at least a portion of the particles have a smooth surface and a tap density equal to or greater than 2.2 g/cm³.

In another aspect, the disclosure is directed to a cathode active material that includes the powders as described herein.

In a further aspect, the disclosure is directed to a cathode having the cathode active material disposed over a current collector.

In another aspect, the disclosure is directed to a battery cell that includes an anode having an anode current collector and an anode active material disposed over the anode current collector and the cathode.

In another aspect, the disclosure is directed to a portable electronic device including a set of components powered by the battery pack.

In another aspect, the disclosure is directed to a method for making a powder described herein. First, a precursor solution (e.g., an aluminum salt and/or fluoride salt precursor) is prepared by dissolving the precursor in a solvent to form a precursor solution. The precursor solution is added to a particle powder to form a wet-impregnated powder. The wet-impregnated powder is heated to an elevated temperature to form a particle having the composition described herein.

In another aspect, multiple precursors (e.g., aluminum salts and fluoride salts) are dissolved in first and second solvents to form first and second solutions, respectively. First and second solutions are then combined to make a precursor solution, which is then added to particles as described herein.

In another aspect, the disclosure is directed to making the particles by dry blending methods. Particles of a nanocrystalline material are combined with particles comprising the compound of Formula (IV). The nanocrystalline material particles and the particles comprising Formula (IV) are subject to a compressive force, shear force, or a combination thereof. The nanocrystalline material particles bond to the surface of the powder particles. The particles thereby form a coating on the powder particles.

In another aspect, the disclosure is directed to compounds represented by Formula (VII) or Formula (VIII):

Li_(α)Co_(1-x-y)M_(y)Mn_(x)O_(δ)  (VII)

Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ)  (VIII)

When the compound is by represented by Formula (VII), in various aspects, M is at least one element selected from B, Na, Mg, Ti, Ca, V, Cr, Fe, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo and Ru. In some variations, 0.95≦α≦1.30, 0<x≦0.30, 0≦y≦0.10, and 1.98≦δ≦2.04. In various aspects, the compound is a single-phase compound with an R3m crystal structure. In further aspects, α>1+x and/or α<1+x.

In further aspects, the disclosure is directed to a powder comprising particles. The mean diameter of the particle can be at least at least 5 μm. In some aspects, the mean diameter of the particle can be at least 20 μm. In some aspects, the particle can comprise secondary particles, each of which comprises a plurality of primary particles sintered together. In some variations the at least 30% of the average secondary particle is formed of a single primary particle.

In further aspects, the disclosure is directed to a cathode active material comprising the compounds or powders.

In further aspects, the disclosure is directed to a battery cell comprising an anode, a cathode comprising a cathode active material. In some aspects, the battery cell can have a first-cycle discharge energy greater than or equal to 750 Wh/kg. In some aspects, the battery cell can have an energy retention greater than or equal to 70% after 10 charge-discharge cycles.

In some aspects, the battery cell can have an energy capacity retention is at least 65% after 52 discharge cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1 is a top-down view of a battery cell in accordance with an illustrative embodiment;

FIG. 2 is a side view of a set of layers for a battery cell in accordance with an illustrative embodiment;

FIGS. 3A-3C are a series of scanning electron micrographs showing, respectively, a base powder, a 0.1 wt. % AlF₃-coated base powder, and a 0.1 wt. % Al₂O₃-coated base powder, according to an illustrative embodiment;

FIG. 4 is a plot of data representing a performance of three coin half cells, each incorporating a single cathode active material, during a first cycle of charging and discharging, according to an illustrative embodiment;

FIG. 5 is a plot of data representing a change in capacity, over extended cycling under rate testing, of the four coin half-cells of FIG. 4, according to an illustrative embodiment;

FIG. 6 is a plot of data representing a change in capacity, over extended cycling under life testing, of the four coin half-cells of FIG. 4, according to an illustrative embodiment;

FIG. 7 is a plot of data representing a change in energy density, over extended cycling under rate testing, of the four coin half-cells of FIG. 4, according to an illustrative embodiment;

FIG. 8 is a plot of data representing a change in energy density, over extended cycling under life testing, of the four coin half-cells of FIG. 4, according to an illustrative embodiment;

FIG. 9 is a plot of data corresponding to charge-discharge profiles for each the four coin half-cells of FIG. 4 under rate testing;

FIG. 10 is a plot of data corresponding to charge-discharge profiles for each the four coin half-cells of FIG. 4 under life testing;

FIG. 11 is a plot of data representing dQ/dV profiles for each the four coin half-cells of FIG. 4 under rate testing; and

FIG. 12 is a plot of data representing dQ/dV profiles for each the four coin half-cells of FIG. 4 under life testing.

FIG. 13 is a plot of data representing an influence of molar ratio on a capacity and efficiency of a cathode active material comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment;

FIG. 14 is a plot of data representing an influence of molar ratio, represented by α, and Mn content, represented by x, on a c-axis lattice parameter of Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment;

FIG. 15 is a plot of data representing a change in the c-axis lattice parameter with molar ratio for Li_(α)Co_(0.96)Mn_(0.04)O₂, according to an illustrative embodiment;

FIG. 16 is a series of scanning electron micrographs of powder prepared at 900° C., 1000° C., 1050° C., and 1100° C., according to an illustrative embodiment;

FIG. 17 is a series of scanning electron micrographs showing an influence of temperature and molar ratio, α, on particle morphology, according to an illustrative embodiment;

FIG. 18 is a plot of data representing an influence of mixing ratio on a capacity and an efficiency of a cathode active material comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment;

FIG. 19 is a series of scanning electron micrographs of cathode active materials comprising Li_(α)Co_(1-x)M_(0.16)O_(δ) and prepared according to a co-precipitation method, according to an illustrative embodiment;

FIG. 20 is a plot of x-ray diffraction patterns of cathode active materials prepared according to a co-precipitation method and comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), Li_(α)Co_(0.90)Mn_(0.10)O_(δ), and Li_(α)Co_(0.84)Mn_(0.16)O_(δ) with varying values of α, according to an illustrative embodiment;

FIG. 21 is a plot of x-ray diffraction patterns of cathode active materials prepared according to a co-precipitation method and comprising Li_(α)Co_(0.78)Mn_(0.22)O_(δ) and Li_(α)Co_(0.72)Mn_(0.28)O_(δ) with varying values of α, according to an illustrative embodiment;

FIG. 22 is a series of scanning electron micrographs of cathode active materials comprising Li_(α)Co_(1-x)M_(x)O_(δ) and prepared according to a sol-gel method, according to an illustrative embodiment;

FIG. 23 is a plot of x-ray diffraction patterns of cathode active materials prepared according to a sol-gel method and comprising Li_(1.131)Co_(0.90)Mn_(0.10)O₂, Li_(1.198)Co_(0.84)Mn_(0.16)O₂, Li_(1.241)Co_(0.78)Mn_(0.22)O₂, and Li_(1.301)Co_(0.72)Mn_(0.28)O₂, according to an illustrative embodiment;

FIG. 24 is a plot of differential capacity curves for cathode active materials comprising LiCoO₂, Li_(1.05)Co_(0.96)Mn_(0.04)O₂, Li_(1.05)Co_(0.93)Mn_(0.07) O₂, Li_(1.05)Co_(0.93)Mn_(0.07)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, and Li_(1.19)Co_(0.72)Mn_(0.28)O₂, according to an illustrative embodiment;

FIG. 25 is a plot of voltage profile curves for cathode active materials comprising Li_(1.05)Co_(0.96)Mn_(0.04)O₂, Li_(1.05)Co_(0.93)Mn_(0.07)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, and Li_(1.19)Co_(0.72)Mn_(0.28)O₂, according to an illustrative embodiment;

FIG. 26 is a contour plot of discharge energy density that varies with Mn substitution, Co_(1-x)Mn_(x), and lithium ratio, [Li]/[Co_(1-x)Mn_(x)], according to an illustrative embodiment;

FIG. 27 a contour plot of energy retention that varies with Mn substitution, Co_(1-x)Mn_(x), and lithium ratio, [Li]/[Co_(1-x)Mn_(x)], according to an illustrative embodiment;

FIG. 28 is a plot of differential capacity curves for cathode active materials comprising Li_(α)Co_(0.99-y)Al_(y)Mn_(0.01)O_(δ), Li_(α)Co_(0.98-y)Al_(y)Mn_(0.02)O_(δ), Li_(α)Co_(0.97-y)Al_(y)Mn_(0.03)O_(δ), and Li_(α)Co_(0.96-y)Al_(y)Mn_(0.04)O_(δ), according to an illustrative embodiment;

FIG. 29 is a plot of differential capacity curves for cathode active materials comprising Li_(0.977)Co_(0.97)Al_(y)Mn_(0.03)O_(δ), Li_(0.992)Co_(0.97)Al_(y)Mn_(0.03)O_(δ), Li_(1.003)Co_(0.97)Al_(y)Mn_(0.03)O_(δ), and Li_(1.014)Co_(0.97)Al_(y)Mn_(0.03)O_(δ), according to an illustrative embodiment;

FIG. 30 is a plot of discharge energy versus cycle count for cathode active materials comprising Li_(0.992)Co_(0.97)Mn_(0.03)O_(δ), Li_(1.003)Co_(0.97)Mn_(0.03) O_(δ), and Li_(1.014)Co_(0.97)Mn_(0.03)O_(δ), according to an illustrative embodiment;

FIG. 31 is a plot of discharge energy versus cycle count for cathode active materials comprising Li_(α)Co_(0.98-y)Al_(y)Mn_(0.02)O_(δ), Li_(α)Co_(0.97-y)Al_(y)Mn_(0.03)O_(δ), and Li_(α)Co_(0.96-y)Al_(y)Mn_(0.04)O_(δ), according to an illustrative embodiment;

FIG. 32 is a plot of nuclear magnetic resonance patterns for Li_(α)Co_(0.97)Mn_(0.03)O_(δ) and Li_(α)Co_(0.97)Mn_(0.03)O_(δ), according to an illustrative embodiment;

FIG. 33 is a plot of discharge energy versus cycle count for cathode, active materials comprising Li_(1.01)Co_(0.97-y)Al_(y)Mn_(0.03)O_(δ) for 0.077, 0.159, and 0.760 wt. % added Al₂O₃, according to an illustrative embodiment

FIG. 34A is a scanning electron micrographs of particles of cathode active material prepared by firing a precursor and comprising Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ), according to an illustrative embodiment;

FIG. 34B is a scanning electron micrograph of the cathode active material of FIG. 34B, but in which the precursor was fired at a higher sintering temperature, according to an illustrative embodiment;

FIG. 35A is a particle size distribution of particles of cathode active material prepared from a precursor fired at 1050° C. and comprising Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ), according to an illustrative embodiment;

FIG. 35B a particle size distribution of particles of cathode active material prepared from a precursor fired at 1085° C. and comprising Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ), according to an illustrative embodiment

FIG. 36 is a plot of surface area change and energy retention versus calcination temperature of a cathode active material comprising Li_(□.01)Co_(1-x-y)Al_(y)Mn_(x)O_(δ), according to an illustrative embodiment;

FIG. 37 is a plot of initial discharge capacity and coulombic efficiency versus calcination temperature of a cathode active material comprising Li_(1.01)Co_(1-x-y)Al_(y)Mn_(n)O_(δ), according to an illustrative embodiment;

FIG. 38 is a plot of heat flow versus calcination temperature of cathode active materials comprising LiCoO₂, Li_(α)Co_(0.99)Mn_(0.01)O_(δ), Li_(α)Co_(0.98)Mn_(0.02)O_(δ), Li_(α)Co_(0.97)Mn_(0.03)O_(δ), Li_(α)Co_(0.96)Mn_(0.04)O_(δ), and Li_(α)Co_(0.93)Mn_(0.07)O_(δ), according to an illustrative embodiment;

FIG. 39 is a plot of c-axis lattice parameter versus lithium content, α, for cathode active materials comprising LiCoO₂, Li_(α)Co_(0.98)Mn_(0.02)O_(δ), Li_(α)Co_(0.97)Mn_(0.03)O_(δ), Li_(α)Co_(0.96)Mn_(0.04)O_(δ), and Li_(α)Co_(0.93)Mn_(0.07)O_(δ), according to an illustrative embodiment;

FIG. 40 is a plot of Raman spectra for cathode active materials comprising LiCoO₂, Li_(α)Co_(0.96)Mn_(0.04)O_(δ), and Li_(α)Co_(0.93)Mn_(0.07)O_(δ), according to an illustrative embodiment;

FIG. 41 is a plot of discharge capacity after 52 cycles versus lithium content, α, of cathode active materials comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), and Li_(α)Co_(0.93)Mn_(0.70)O_(δ), according to an illustrative embodiment;

FIG. 42 is a plot of differential capacity curves for cathode active materials comprising Li_(1.025)Co_(0.96-y)Al_(y)Mn_(0.04)O_(δ), and Li_(1.00)Co_(0.93-y)Al_(y)Mn_(0.07)O_(δ), according to an illustrative embodiment; and

FIG. 43 is a data plot of first-cycle charge capacity, first-cycle discharge capacity, and first cycle coulombic efficiency versus lithium content, a, for cathode active materials comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. Thus, the disclosure is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

As used herein, all compositions referenced for cathode active materials represent those of as-prepared materials (i.e., “virgin” materials) unless otherwise indicated. Materials of these compositions have not yet been exposed to additional processes, such as de-lithiation and lithiation during, respectively, charging and discharging of a lithium-ion battery.

Lithium cobalt oxides can be used in cathode active materials for commercial lithium-ion batteries. These compounds often include lithium cobalt oxide or derivatives thereof. The performance of such cathode active materials can be increased by improving its capacity, working voltage, and gravimetric electrode density.

The morphology of particles can also influence the performance of cathode active materials. Particles can include primary and secondary particles. Primary particle and secondary particle size distribution, shape, and porosity can impact the density of lithium cobalt oxide electrodes. Secondary particles are comprised of agglomerates of the smaller, primary particles, which are also often referred to as grains. Control of the secondary particle characteristics of shape and density can be gained.

The performance of batteries can be improved using compounds and particles that provide increased capacity, working voltage, and gravimetric electrode density. These and other needs are addressed by the disclosure herein.

FIG. 1 presents a top-down view of a battery cell 100 in accordance with an embodiment. The battery cell 100 may correspond to a lithium-ion or lithium-polymer battery cell that is used to power a device used in a consumer, medical, aerospace, defense, and/or transportation application. The battery cell 100 includes a stack 102 containing a number of layers that include a cathode with a cathode active coating, a separator, and an anode with an anode active coating. More specifically, the stack 102 may include one strip of cathode active material (e.g., aluminum foil coated with a lithium compound) and one strip of anode active material (e.g., copper foil coated with carbon). The stack 102 also includes one strip of separator material (e.g., conducting polymer electrolyte) disposed between the one strip of cathode active material and the one strip of anode active material. The cathode, anode, and separator layers may be left flat in a planar configuration or may be wrapped into a wound configuration (e.g., a “jelly roll”).

Battery cells can be enclosed in a flexible pouch. Returning to FIG. 1, during assembly of the battery cell 100, the stack 102 is enclosed in a flexible pouch. The stack 102 may be in a planar or wound configuration, although other configurations are possible. The flexible pouch is formed by folding a flexible sheet along a fold line 112. For example, the flexible sheet may be made of aluminum with a polymer film, such as polypropylene. After the flexible sheet is folded, the flexible sheet can be sealed, for example, by applying heat along a side seal 110 and along a terrace seal 108. The flexible pouch may be less than 120 microns thick to improve the packaging efficiency of the battery cell 100, the density of battery cell 100, or both.

The stack 102 also includes a set of conductive tabs 106 coupled to the cathode and the anode. The conductive tabs 106 may extend through seals in the pouch (for example, formed using sealing tape 104) to provide terminals for the battery cell 100. The conductive tabs 106 may then be used to electrically couple the battery cell 100 with one or more other battery cells to form a battery pack.

Batteries can be combined in a battery pack in any configuration. For example, the battery pack may be formed by coupling the battery cells in a series, parallel, or a series-and-parallel configuration. Such coupled cells may be enclosed in a hard case to complete the battery pack, or may be embedded within an enclosure of a portable electronic device, such as a laptop computer, tablet computer, mobile phone, personal digital assistant (PDA), digital camera, and/or portable media player.

FIG. 2 presents a side view of a set of layers for a battery cell (e.g., the battery cell 100 of FIG. 1) in accordance with the disclosed embodiments. The set of layers may include a cathode current collector 202, a cathode active coating 204, a separator 206, an anode active coating 208, and an anode current collector 210. The cathode current collector 202 and the cathode active coating 204 may form a cathode for the battery cell, and the anode current collector 210 and the anode active coating 208 may form an anode for the battery cell. To create the battery cell, the set of layers may be stacked in a planar configuration, or stacked and then wrapped into a wound configuration.

As mentioned above, the cathode current collector 202 may be aluminum foil, the cathode active coating 204 may be a lithium compound, the anode current collector 210 may be copper foil, the anode active coating 208 may be carbon, and the separator 206 may include a conducting polymer electrolyte.

It will be understood that the cathode active materials described herein can be used in conjunction with any battery cells or components thereof known in the art. For example, in addition to wound battery cells, the layers may be stacked and/or used to form other types of battery cell structures, such as bi-cell structures. All such battery cell structures are known in the art.

Surface-modified and structure-stabilized lithium cobalt oxide materials are disclosed. The materials can be used as cathode active materials in lithium-ion batteries.

In various aspects, the transition-metal oxides are variations of lithium cobalt oxides. In one aspect, the disclosure is directed to compounds of Formula (I):

Li_(α)MO_(δ)  (I)

wherein M=Co, Mn, Ni, or any combination thereof, 0.95≦α≦2, and 2≦δ≦3. In some variations, 1≦α≦2. In some variations, 1.20≦α. In some variations, 1.40≦α. In some variations, 1.60≦α. In some variations, 1.80≦α. In some variations, α≦1.8. In some variations, α≦1.6. In some variations, α≦1.4. In some variations, α≦1.2. In some variations, α≦1.8. Further, in some variations, 2.2≦δ. In some variations, 2.4≦δ. In some variations, 2.6≦δ. In some variations, 2.8≦δ. In some variations, δ≦2.8. In some variations, δ≦2.6. In some variations, δ≦2.4. In some variations, δ≦2.2. It will be understood that the boundaries of a and g can be combined in any variation as above.

In various aspects, the disclosure is directed to compounds of Formula (IIa):

(x)[Li₂M¹O₃].(1-x)[LiM²O₂]  (IIa)

wherein M¹ is one or more cations with an average oxidation state of 4+ (i.e., tetravalent), M² is one or more cations with an average oxidation state of 3+ (i.e., trivalent), and 0≦x≦1. In some variations, M¹ is selected from Ti, Mn, Zr. Mo, Ru, and a combination thereof. In specific variations, M¹ is Mn. In some variations, M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Ru, Mo and a combination thereof. In some variations, M² is selected from Mg, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, and a combination thereof. In specific variations, M² is Co.

It will be appreciated that, in the representation for excess-lithium transition-metal oxides, M=[M²]_(1-x)[M¹]_(x), α=1+x, and δ=2+x. In some variations, α≦1.2. In some variations, α≦1.4. In some variations, α≦1.6. In some variations, α≦1.8. In some variations, 1.2≦α. In some variations, 1.4≦α. In some variations, 1.6≦α. In some variations, 1.8≦α. It will be understood that the boundaries of x can be combined in any variation as above. For the embodiments disclosed herein, cobalt is a predominant transition-metal constituent which allows high voltage, and high volumetric energy density for cathode active materials employed in lithium-ion batteries.

In various aspects, the disclosure is directed to compounds of Formula (IIb):

(x)[Li₂M¹O₃].(1-x)[Li_(1-y)M²O₂]  (IIb)

wherein M¹ is one or more cations with an average oxidation state of 4+ (i.e., tetravalent), M² is one or more cations, 0≦x≦1, and 0≦y≦1. In some variations, M¹ is selected from Ti, Mn, Zr, Mo, Ru, and a combination thereof. In specific variations, M¹ is Mn. In some variations, M² is selected from B, Na, Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Ru, Mo and a combination thereof. In some variations, M² is selected from Mg, Ti, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, and a combination thereof. In some variations, M² is selected from Mg, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, and a combination thereof. In specific variations, M² is Co and Mn.

It will be appreciated that, in the representation for excess-lithium transition-metal oxides, M=[M²]_(1-x)[M¹]_(x), α=1+x−y+xy, and δ=2+x. In some variations, α≦0.98. In some variations, α≦1.0. In some variations, α≦1.1. In some variations, α≦1.2. In some variations, 0.95≦α. In some variations, 1.3≦α. In some variations, 1.6≦α. In some variations, 1.8≦α. It will be understood that the boundaries of a can be combined in any variation as above. For the embodiments disclosed herein, cobalt is a predominant transition-metal constituent which allows high voltage, and high volumetric energy density for cathode active materials employed in lithium-ion batteries.

In some variations, the disclosure is directed to a compound represented by Formula (III):

Li_(α)Co_(1-x)M_(x)Al_(γ)O_(δ)  (III)

wherein M is B, Na, Mn, Ni, Mg, Ti, Ca, V, Cr, Fe, Cu, Zn, Al, Sc, Y, Ga, Zr, Mo, Ru or a combination thereof or any combination thereof; 0.95≦α≦1.10; 0≦x≦0.50; 0≦γ≦0.05; and 1.95≦δ≦2.60. In some variations, M is Mn, Ni, or any combination thereof. In some variations, M is Mn, Ni, or a combination thereof, 0.95≦α≦1.10, 0<x<0.50, 0≦γ≦0.05, and 1.95≦δ≦2.60. In some variations, 0.01≦γ≦0.03. In some variations, 0.001≦γ≦0.005. In some variations, 0.002≦γ≦0.004. In some variations, γ is 0.003. In some variations, 0.02≦γ≦0.03. In such variations of Formula (III) where γ≠0 (i.e., aluminum is present), a distribution of aluminum within the particle may be uniform or may be biased to be proximate to a surface of the particle. Other distributions of aluminum are possible. In some variations, Al is at least 500 ppm. In some variations, Al is at least 750 ppm. In some variations, Al is at least 900 ppm. In some variations, Al is less than or equal to 2000 ppm. In some variations, Al is less than or equal to 1500 ppm. In some variations, Al is less than or equal to 1250 ppm. In some variations, Al is approximately 1000 ppm.

In additional variations of Formula (III), 1.02≦α≦1.05 and 0.02≦x≦0.05. In further variations of Formula (III), 1.03≦α≦1.05 and x=0.04. It will be recognized that the components as described above can be in any combination.

The various compounds of Formulae (I), (IIa), (IIb), and (III) can include Mn⁴⁺. Without wishing to be limited to any theory or mode of action, incorporating Mn⁴⁺ can improve a stability of oxide under high voltage charging (e.g., 4.5V) and can also help maintain an R3m crystal structure (i.e., the α-NaFeO₂ structure) when transitioning through a 4.1-4.3V region (i.e., during charging and discharging).

In some embodiments, the disclosure is directed to a powder that includes particles. In some aspects, the particles can comprise the compound of Formula (III) and new formula. In some variations, the particles comprise a core comprising a compound of Formula (I), Formula (IIa), Formula (IIb) or Formula (III), and a coating disposed over at least a portion of the core. In further variations, the particles comprise a core comprising a compound of Formula (III), and a coating disposed over at least a portion of the core.

It will be appreciated that the powder may serve as a part or all of a cathode active material. The particles described herein can be used in a cathode active material in a battery. Such cathode active materials can tolerate voltages equal to or higher than conventional materials (i.e., relative to a Li/Li⁺ redox couple) without capacity fade. Capacity fade degrades battery performance and may result from a structural instability of the cathode active material, a side reaction with electrolyte at high voltage, surface instability, a dissolution of cathode active material into the electrolyte, or some combination thereof.

In variations in which the particles comprise compounds of Formula (III) and contain aluminum, the aluminum can be referred to as a dopant. Such aluminum dopants can be distributed uniformly throughout the particle, or alternatively localized along the surface of the particle.

In further variations, the particle comprises a core and a coating. The coating can be an oxide material, a fluoride material, or a combination thereof. In some variations, the coating may be a layer of material in contact with a surface of the core or a reaction layer formed along the surface of the core. The coating can include an oxide material (e.g., ZrO₂, Al₂O₃, etc.), a fluoride material (e.g., AlF₃), or a combination thereof (e.g., AlO_(x)F_(y)). In some embodiments, the oxide material includes at least one element selected from the group consisting of Al, Co, Li, Zr, Mg, Ti, Zn, Mn, B, Si, Ga, and Bi. In these embodiments, the oxide material may include oxoanions such as phosphates (e.g., AlPO₄, Co₃(PO₄)₂, LiCoPO₄, etc.). In some embodiments, the fluoride material includes at least one element selected from the group consisting of Al, Co, Mn, Ni, Li, Ca, Zr, Mg, Ti, and Na. The coating may include one or more compositions selected from AlF₃, Al₂O₃, AlPO₄, Co₃(PO₄)₂, LiCoPO₄, and ZrO₂.

The coating can be in any amount known in the art. In some variations, amount of coating may be less than or equal to 7 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 5 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.8 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.6 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.4 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.3 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.2 wt. % of the total particle. In some variations, amount of coating may be less than or equal to 0.1 wt. % of the total particle. In various aspects, the amount can be chosen such that a capacity of the cathode active material is not negatively impacted.

The coating may include multiple layers of coating material. The coating may also be a continuous coating or a discontinuous coating. Non-limiting examples of discontinuous coatings include coatings with voids or cracks and coatings formed of particles with gaps therebetween. Other types of discontinuous coatings are possible.

Powders comprising the particles described herein can be used as a cathode active material in a lithium ion battery. Such cathode active materials can tolerate voltages equal to or higher than conventional materials (i.e., relative to a Li/Li⁺ redox couple) without capacity fade. Capacity fade degrades battery performance and may result from a structural instability of the cathode active material, a side reaction with electrolyte at high voltage, surface instability, dissolution of cathode active material into the electrolyte, or some combination thereof.

In various aspects, the compounds and/or particles as described herein, when incorporated into a battery as a cathode active material, have lithium ion batteries that can be charged at high voltages without capacity fade. Without wishing to be held to a specific mechanisms or mode of action, the compounds may impede or retard structural deviations from an α-NaFeO₂ crystal structure during charging to at higher voltages.

In various aspects, the compounds as described herein, when incorporated into a battery as a cathode active material, have lithium ion batteries to have voltages greater than 4.2V without capacity fade. In further aspects, such batteries have voltages greater than 4.3V. In various aspects, the lithium cobalt oxide materials are directed to voltages greater than 4.4V. In various aspects, the lithium cobalt oxide materials are directed to voltages greater than 4.5V.

Batteries having cathode active materials that include the disclosed particles can show improved the battery performance at high voltages. For example, the particles provide for an increased battery capacity over cycles at high voltage (e.g., 4.5V). In certain variation, the decay rate of the battery is less than 0.7 mAh/g/cycle at a charge potential of 4.5V. In some variations, the decay rate of the battery is less than 0.6 mAh/g/cycle at a charge potential of 4.5V. In some variations, the decay rate of the battery is less than 0.5 mAh/g/cycle at a charge potential of 4.5V.

In some additional variations, batteries that include cathode active materials comprising the disclosed particles lose lower amounts of energy per unit mass per cycle. In some embodiments, such batteries lose less than 4 Wh/kg over per cycle when operated at a potential of 4.5V. The disclosure is further directed to methods of making the disclosed compounds and particles.

In embodiments in which the particle or core comprises compounds of Formula (VI), Al may be introduced via a surface modification process. For example, and without limitation, the particle may be coated with a coating comprising aluminum and subsequently heated. Thermal energy can enable a reaction between the particle and the coating, thereby infusing aluminum into the core (e.g., doping). In another non-limiting example, the particle may be exposed to a solution that comprises aluminum. A chemical reaction between the particle and the solution can create a surface reaction layer comprising aluminum. The particle may be subsequently heated (e.g., to diffuse aluminum from the surface reaction layer into the particle, convert the surface reaction layer into a coating, etc.). In a further non-limiting example, the particle may be contacted with particles that comprise aluminum, such as during milling. Mechanical energy creates compressive forces, shear forces, or a combination thereof, to fuse the aluminum particles to the particle (e.g., bond Al₂O₃ nanoparticles to the particle). These surface modification processes can allow the core to achieve an aluminum content between 0≦γ≦0.03. Other surface modification processes are possible.

In various embodiments, the performance of batteries including the compounds and/or powders can increase battery capacity and/or reduce the loss of available power in a fully charged battery over time.

The disclosure is further directed to methods of modifying a surface of particles by wet processing or dry processing.

In one aspect, the disclosure is directed to methods of making particles. A precursor solution comprising a first amount of a precursor dissolved in a solvent is prepared. The powders comprises a compound according to Formula (I), (IIa), (IIb) or (III). The precursor solution is added to the powder to form a wet-impregnated powder. The wet-impregnated powder is heated to an elevated temperature.

In another aspect, the first precursor is dissolved in a first portion of the solvent to form a first solution. The first solution is added to the powder to form a partial wet-impregnated powder. A second precursor is dissolved into a second portion of solvent to form a second solution. The second is added to the partial wet-impregnated powder to produce a wet-impregnated powder. The wet-impregnated powder is then heated at an elevated temperature.

Wet-impregnation involves adding solvent to particles of the powder until the particles exhibit a damp consistency (e.g., paste-like). In various aspects, the amount of solvent can be selected such that, when the precursor solution is added to the powder, the wet-impregnated powder so-produced exhibits a damp consistency. The method additionally includes heating the wet-impregnated powder at an elevated temperature. It will be appreciated that the amount of solvent may be determined by selecting a known amount of the powder and progressively adding solvent until all particles of the powder appear wet, but do not flow (i.e., show a damp consistency). A ratio of solvent to powder (e.g., grams of solvent per grams of the powder) may be scaled as needed to accommodate different amounts of the powder when utilizing the method. A concentration of the at least one precursor may then be selected to apply a desired quantity of material onto the surface of the particles. Representative variations of the method are described in relation to Examples 1, 3, 4, 5, and 6.

In some embodiments, heating the wet-impregnated powder includes drying the wet-impregnated powder. In some embodiments, the at least one precursor includes aluminum (e.g., see Example 1).

In some embodiments, preparing the precursor solution includes dissolving a first precursor into a first portion of solvent to form a first solution and dissolving a second precursor into a second portion of solvent to form a second solution. The first portion of solvent and the second portion of solvent, in total, may correspond to the amount of solvent. In these embodiments, preparing the precursor solution also includes mixing the first solution with the second solution, thereby forming the precursor solution. In some instances, the first precursor includes aluminum and the second precursor includes phosphate (e.g., see Example 3). In other instances, the first precursor includes cobalt and the second precursor includes phosphate (e.g., see Example 4). In still other instances, the first precursor include aluminum and the second precursor includes lithium (e.g., see Example 5).

In some embodiments, preparing the precursor solution includes dissolving the first precursor into the first portion of solvent to form the first solution, dissolving the second precursor into the second portion of solvent to form the second solution, and dissolving a third precursor into a third portion of solvent to form the third solution. The first portion of solvent, the second portion of solvent, and the third portion of solvent, in total, correspond to the amount of solvent. In such embodiments, preparing the precursor solution also includes mixing the first solution, the second solution, and the third solution thereby forming the precursor solution.

In some embodiments, at least one of the first precursor, the second precursor, and the third precursor include lithium. In some embodiments, the first precursor includes cobalt, the second precursor includes lithium, and the third precursor includes phosphate (e.g., see Example 6).

In some embodiments, adding the first solution to the powder includes drying the partial wet-impregnated powder. In some embodiments, heating the wet-impregnated powder includes drying the wet-impregnated powder. In some embodiments, the first precursor includes aluminum and the second precursor include fluorine (e.g., see Example 2).

According to an illustrative embodiment, a method for modifying a surface of particles includes stirring a suspension of particles. The particles include the compound of Formula (III). The method also involves adding one or more precursor to the suspension of particles while stirring. In some embodiments, the method additionally includes filtering the particles after adding the precursor solution. Representative variations of the method are described in relation to Examples 7-9.

In some embodiments, the method includes filtering the particles after adding the at least one precursor and heating the filtered particles to an elevated temperature. In some embodiments, the precursor solution can include aluminum or cobalt (e.g., see Example 8). Non-limiting examples of the metal precursor include an aluminum precursor, e.g., Al(NO₃)₃, and a cobalt precursor, e.g., Co(NO₃)₃.

According to an illustrative embodiment, a method for modifying a surface of particles in a powder includes blending particles of nanocrystalline material with particles of the powder. The particles of the powder can include a compound according to Formula (I), (IIa), or (III), as described herein. The particles can be combined with the nanocrystalline material and while blending, and/or subjected to compressive forces, shear forces, or a combination thereof. Such forces can induce the nanocrystalline material particles to bond to surfaces of the particles of the powder. The nanocrystalline material particles and the powder particles can be blended in such a ratio that the nanocrystalline material particles form a predetermined amount of coating on the powder particles. Representative variations of the method are described in relation to Examples 10-12. In some embodiments, the nanocrystalline material particles can include an aluminum oxide material, an aluminum fluoride material, or a combination thereof.

In some variations, the disclosure is directed to a compound represented by Formula (IV):

Li_(α)Co_(1-x)Mn_(x)O_(δ)  (IV)

wherein 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20. In some variations, 0.98≦α≦1.01. In some variations of Formula (IV), 0.98≦α≦1.01 and x=0.03. In some variations of Formula (IV), 1.00≦α≦1.05. In some variations, 0<x≦0.10. In a further variations, the disclosure is directed to a compound represented by Formula (IV), wherein 0.95≦α≦1.05 and 0.02≦x≦0.05. In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.95≦α≦1.05 and x=0.04. In some variations, x=0.03. In further variations of Formula (IV), 1.01≦α≦1.05 and 0.02≦x≦0.05. In still further variations of Formula (IV), 1.01≦α≦1.05 and x=0.04. In some variations of Formula (IV), 1.00≦α≦1.10. In other variations of Formula (IV), 1.00≦α≦1.05. In a further aspect, the disclosure is directed to a compound represented by Formula (IV), wherein 0.98≦α≦1.01, x=0.03, and δ=2.

It will be appreciated that α represents a molar ratio of lithium content to total transition-metal content (i.e., total content of Co and Mn). In various aspects, increasing lithium content can increase capacity, improve stability, increase gravimetric density of particles comprising the compound, increase particle density, and/or increase particle strength of the cathode active material. In various aspects, decreasing lithium content can increase capacity, improve stability, increase gravimetric density of particles comprising the compound, increase particle density, and/or increase particle strength of the cathode active material.

In some variations, the compound of Formula (IV) may be represented as a solid solution of two phases, i.e., a solid solution of Li₂MnO₃ and LiCoO₂. In these variations, the compound may be described according to Formula (Va):

(x)[Li₂MnO₃].(1-x)[LiCoO₂]  (Va)

where Mn is a cation with an average oxidation state of 4+ (i.e., tetravalent) and Co is a cation with an average oxidation state of 3+ (i.e., trivalent). A more compact notation for Formula (Va) is given below:

Li_(1+x)Co_(1-x)Mn_(x)O_(2+x)  (VI)

In Formula (VI), x describes including both Mn and Co. Due to differing valences between Mn and Co, such inclusion of Mn may influence lithium content and oxygen content of the compound.

In Formula (IV), the composition of ‘x’ can be 0≦x≦0.10. In some variations, 0<x≦0.10. In such variations, the lithium content can be from 1 to 1.10 in Formula (VI), and the oxygen content can be from 2 to 2.10. However, the compounds disclosed herein have lithium contents and oxygen contents that may vary independently of x. For example, and without limitation, the lithium and oxygen contents may vary from stoichiometric values due to synthesis conditions deliberately selected by those skilled in the art. As such, subscripts in Formulas (V) and (VI) are not intended as limiting on Formula (IV), i.e., α is not necessarily equal to 1+x, and δ is not necessarily equal 2+x. It will be appreciated that the lithium content and the oxygen content of compounds represented by Formula (IV) can be under-stoichiometric or over-stoichiometric relative to the stoichiometric values of Formula (VI).

In some variations, the compound of Formula (IV) may be represented as a solid solution of two phases, i.e., a solid solution of Li₂MnO₃ and LiCoO₂. In these variations, the compound may be described according to Formula (Vb):

(x)[Li₂MnO₃].(1-x)[Li_((1-y))Co_((1-y))Mn_(y)O₂]  (Vb)

where Mn is a cation with an average oxidation state of 4+ (i.e., tetravalent) and Co is a cation with an average oxidation state of 3+ (i.e., trivalent).

The disclosure is further directed to powders comprising compounds described herein. In various aspects, the disclosure is directed to a powder that includes particles comprising Li_(α)Co_(1-x)Mn_(x)O_(δ) where 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20. In some variations, 0<y≦0.10. The powder may serve as part or all of a cathode active material (i.e., the cathode active material includes the powder). In some embodiments, 0.98≦α≦1.01 and x=0.03. In some embodiments, 1.00≦α≦1.05. In further embodiments, 1.01≦α≦1.05 and 0.02<x<0.05. In still further embodiments, 1.01≦α≦1.05 and x=0.04. In some embodiments, 1.00≦α≦1.10. In other embodiments, 1.00≦α≦1.05.

In some variations, the compound of Formula (IV) may be represented as a solid solution of two phases, i.e., a solid solution of Li₂MnO₃ and LiCoO₂. In these variations, the compound may be described according to Formula (Va) or Formula (Vb), where Mn is a cation with an average oxidation state of 4+ (i.e., tetravalent) and Co is a cation with an average oxidation state of 3+ (i.e., trivalent).

Alternatively, a more compact notation is depicted as Formula (Vc):

Li_(1+x-y-xy)Co_((1-x))*_((1-y))Mn_((x+y-x)*_(y))O_(2+x)  (Vc)

In Formula (Vc), x can describe both Mn and Co. Without wishing to be held to a particular mechanism or mode of action, because of differing valences between Mn and Co, inclusion of Mn may influence lithium content and oxygen content of the compound.

In Formula (Vc), the combination of ‘x’ and ‘y’ at least zero and less than or equal to 0.10. In some variations, the combination of ‘x’ and ‘y’ can be greater than zero and less than or equal to 0.10. In such variations, the lithium content can be any range described herein for other Formulae. In some variations, Li can be from 0.9 to 1.10. In some variations, oxygen content can be from 2 to 2.10. It will be recognized that, as with all Formulae presented herein, that the compounds disclosed herein have lithium contents and oxygen contents that may vary independently of x and y.

The compounds and powders can be in a cathode active material for lithium ion batteries, as described herein. These cathode active materials assist energy storage by releasing and storing lithium ions during, respectively, charging and discharging of a lithium-ion battery.

Without wishing to be limited to a specific mechanism or mode of action, the characteristics of the powder can provide improved battery performance when the powder is used as a cathode active material. Powders comprising the compounds described herein have increased tap densities over previously known compounds. Batteries comprising these powders as a cathode active material have an increased volumetric energy density.

In some instances, batteries having such cathode active materials have a specific capacity greater than 130 mAh/g. In some instances, the specific capacity is greater than 140 mAh/g. In some instances, the specific capacity is greater than 150 mAh/g. In some instances, the specific capacity is greater than 160 mAh/g. In some instances, the specific capacity is greater than 170 mAh/g.

Increasing an initial lithium content in the cathode active materials (e.g., an as-prepared lithium content) can increase the volumetric energy density and/or cycle life.

The cathode active material can exhibit a high tap density and/or improved particle strength. In some instances, the cathode active material can exhibit a tap density equal to or greater than 2.1 g/cm³. In some instances, the cathode active material can exhibit a tap density equal to or greater than 2.2 g/cm³. In some instances, the cathode active material can exhibit a tap density equal to or greater than 2.3 g/cm³. In some instances, the cathode active material can exhibit a tap density greater than or equal to 2.4 g/cm³.

In some variations, the disclosure is directed to a cathode active material for lithium-ion batteries that includes a lithium cobalt oxide having a tetravalent metal of Mn⁴⁺. In these materials, the trivalent Co ion, Co³⁺, can serve as host to supply the capacity. Without wishing to be limited to any theory or mode of action, incorporating Mn⁴⁺ can improve a stability of lithium cobalt oxide under high voltage charging and can also help maintain an R3m crystal structure when transitioning through a 4.1-4.6 V region (i.e., during charging and discharging).

In some instances, the voltage charge can be equal to or greater than 4.4 V. In some instances, the voltage charge can be equal to or greater than 4.5 V. In some instances, the voltage charge can be equal to or greater than 4.6 V.

A degree of Mn can influence an amount of additional lithium desired for the cathode active material. For example, and without limitation, a composition of lithium cobalt oxide having 92% Co and 8% Mn may correspond to a lithium content of 6 to 10 mole percent in excess of unity. In general, however, ranges for the lithium content may vary based on the degree of manganese substitution, and as shown in relation to FIG. 13, may be determined by those skilled in the art using empirical data.

FIG. 13 presents a plot of data representing an influence of molar ratio on a capacity (i.e., a first-cycle discharge capacity) and efficiency of a cathode active material comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ) (i.e., x=0.04), according to an illustrative embodiment. The molar ratio, indicated on the abscissa, corresponds to α, the molar ratio of lithium content to total transition-metal content (i.e., described as the “Li/TM ratio” in FIG. 13). To determine the molar ratio, the cathode active material was characterized chemically using inductively-coupled plasma optical emission spectroscopy (ICP-OES), as known to those skilled in the art. The capacity and efficiency are indicated, respectively, on the left-side and right-side ordinates.

With further reference to FIG. 13, a first curve 300 representing a change in capacity with the molar ratio is fitted to a first set of data points 302. A second curve 304 representing a change in efficiency with the molar ratio is fitted to a second set of data points 306. For this particular composition (i.e., x=0.04), the first curve 300 exhibits a maximum in a range corresponding to 0.98≦α≦1.05. However, it will be appreciated that limits of the range may change in response to changes in x, which represents an amount of Mn in the cathode material. In general, those skilled in the art may alter a and x to achieve a desired combination of capacity and efficiency.

In certain variations, the compounds described herein can allow for excess lithium storage. In FIG. 13, increasing lithium (i.e., 0.98≦α≦1.05) is demonstrated to increase the capacity of the cathode material relative to unity (i.e., α=1.00). This increased capacity allows those skilled in the art to match a particular (increased) capacity to a desired efficiency. Such increased capacity is unexpected. In various aspects, additional lithium can normally expected to function as a contaminant in the cathode material, degrading its performance. Indeed, when the excess of lithium exceeds a threshold value (e.g., exceeds a 1.05 in FIG. 13), both capacity and efficiency decrease.

In various aspects, the compounds described herein provide for increased capacity and stability of the cathode active material over known compounds. FIG. 14 presents a plot of data representing an influence of the molar ratio, represented by α, and Mn content, represented by x, on a c-axis lattice parameter of the compound of Formula (IV), i.e., Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment. Oxygen in the composition may correspond to δ=2, although variations from this stoichiometry are possible (i.e., within 1.90≦δ≦2.20). The data are generated using techniques of X-ray diffraction, as known by those skilled in the art. The (003) peak in the R3m diffraction pattern for LiCoO₂ characteristically shifts according x and α. For a given x (e.g., 0.04 or 4 mole percent), the c-lattice contracts with increasing α (i.e., as α increases from 1.0062 to 1.0925). Without wishing to be limited to any theory or mode of action, it is believed that excess Li moves into a transition metal layer of Li_(α)Co_(0.96)Mn_(0.04)O_(δ) due to the presence of Mn⁴⁺. This displacement increases the lithium capacity and stability of the material.

FIG. 15 presents a plot of data representing a change in the c-axis lattice parameter with molar ratio for Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment. (The molar ratio, α, is indicated on the abscissa as “ICP Li/TM”). Oxygen in the composition may correspond to δ=2, although variations from this stoichiometry are possible (i.e., within 1.90≦δ≦2.20). To determine α, the cathode active material was characterized chemically using ICP-OES, as known to those skilled in the art. The change in the c-axis lattice parameter follows a sigmoidal curve. The sigmoidal curve tends to become asymptotic at extremes of a (i.e., the lowest and highest values of α shown in FIG. 15).

The disclosure is further directed to methods of producing a powder comprising Li_(α)Co_(1-x)Mn_(x)O_(δ). The method includes the steps of mixing a lithium source with precursor particles to produce a reactant, and then heating the reactant to a high temperature.

Precursors of the lithium-ion cathode materials can be calcined to obtain the positive electrode material. However, it can be difficult to control the particle sintering process to produce high density particles and at the same time produce a high capacity material. State of the art procedures add a variable amount of extra lithium of up to 10 wt % due to its high evaporation rate at high temperatures.

The precursor particles comprise a transition-metal hydroxide comprising Co and Mn. Non-limiting examples of the lithium source include lithium hydroxide (i.e., LiOH) and lithium carbonate (i.e., Li₂Co₃). However, other lithium sources are possible.

The method also includes heating the reactant to a temperature equal to or greater than 800° C. In these methods, 0≦x≦0.10 and 1.90≦δ≦2.20. In some variations, 0<x≦0.10. The ratio of the lithium source to the precursor particles is selected such that 0.95≦α≦1.10. This ratio may be equal to or greater than the molar ratio, α, due to evaporative losses of lithium during heating. In some embodiments, the temperature is between 800-1200° C.

In some aspects, the temperature of heating is from about 800 to about 1000° C. In other aspects, the temperature of heating is from about 1000 to about 1100° C. In other aspects, the temperature of heating is from about 1100 to about 1200° C. In still other aspects, the temperature of heating is from about 900 to about 1000° C. In still yet other aspects, the temperature of heating is from about 800 to about 900° C. Without wishing to be limited to any mechanism or mode of action, temperatures in the aforementioned ranges allow particles of powder to exhibit gravimetric density and strength sufficient for lithium-ion battery applications. These ranges also correspond to improved capacities and first-cycle efficiencies. Again, without wishing to be limited to any mechanism or mode of action, it will be appreciated that high gravimetric densities allow increased energy densities for the cathode active material. Particle strength can improve efficient handling during battery manufacturing and for cycle stability during battery operation.

In various aspects, the molar ratio (i.e., a), the temperature, and corresponding heating periods can control particle sintering and densification. FIG. 16 presents a series of scanning electron micrographs of powder prepared at 900° C., 1000° C., 1050° C., and 1100° C., according to an illustrative embodiment. The temperature increases from left to right and a magnification increases from top to bottom. A composition of the powder particles corresponds to α=1.04 and x=0.04. At 900° C. and 1000° C., particles of the powder retain a plate-like structure of the precursor particles. The powder exhibits a tap density of 2.0 and 2.1 g/cm³, respectively. At 1050° C. and 1100° C., however, a morphology of individual particles in the powder has changed to smooth (i.e., a smooth surface). This smooth morphology suggests a partial melting during. The corresponding tap density increases to 2.3-2.4 g/cm³. These powders show greater strength because the grains (i.e., the primary particles) have grown and are better bonded together. Moreover, the grains have decreased in number and fewer grain boundaries are present therein.

In these methods, additional lithium content controls a degree of sintering of the precursor particles. Such additional lithium content also controls a capacity of the powder, when included as a cathode active material. It will be understood that sufficient lithium should be present to react with and sinter the precursor particles, but not risk over-sintering the precursor particles. Over-sintering can produce a solid mass. Even if a solid mass can be avoided, excessive lithium may lower capacity and efficiency of the cathode active material.

The particle density and strength increases with increasing molar ratio (i.e., α). FIG. 17 presents a series of scanning electron micrographs showing an influence of temperature and molar ratio (α) on particle morphology, according to an illustrative embodiment. A composition of the powder (i.e., particles therein) corresponds to x=0.04 with α increasing progressively from 1.00, to 1.04, to 1.06, to 1.08, and to 1.10 (i.e., from left to right in FIG. 17). Two temperatures are presented, i.e., 1050° C. and 1100° C. Oxygen in the composition may correspond to δ=2, although variations from this stoichiometry are possible (i.e., within 1.90≦δ≦2.20).

The heating temperature can have an effect on the surface morphology and increased tap density of the powder. In the embodiment depicted in FIG. 17, at 1050° C. and a values less than 1.02 the secondary particles are free-flowing after calcination. However, primary grains are not well bonded for strength. At higher molar ratios, however, individual grains fused together better. At 1100° C., the secondary particles had smooth surfaces and well-bonded grains. As the molar ratio is increased (i.e., at 1100° C.), the secondary particles begin to bond together, forming a rigid sintered mass of particles. This rigid sintered mass may be broken apart by grinding.

In some embodiments, 1.00≦α≦1.05. In other embodiments of the method, 1.00<α≦1.10. In further embodiments, 1.00≦α≦1.05.

In some embodiments, 1.01≦α≦1.05 and 0.02≦x≦0.05. In further embodiments, 1.01≦α≦1.05 and x=0.04.

FIG. 18 presents a plot of data representing an influence of mixing ratio on a capacity and an efficiency of a cathode active material comprising Li_(α)Co_(0.96)Mn_(0.04)O_(δ), according to an illustrative embodiment. The mixing ratio corresponds to the ratio of lithium source mixed the precursor particles. The cathode active material includes the powder depicted in FIG. 17 and calcined at 1050° C. Oxygen in the composition may correspond to δ=2 although variations from this stoichiometry are possible (i.e., within 1.90≦δ≦2.20).

In FIG. 18, the abscissa shows an increase of the mixing ratio from 1.00 to 1.10. The cathode active material has a maximum discharge capacity of 192 mAh/g (i.e., during discharge from 4.5 V to 2.75 V) at a mixing ratio of 1.04, which corresponds to α=1.01 as measured by ICP-OES. High discharge values of 190 mAh/g for mixing ratios of 1.06, 1.08, and 1.10 (i.e., α=1.02, 1.03, and 1.04, respectively by ICP-OES) can also be obtained.

In some variations, the disclosure is directed to a compound represented by Formula (VII):

Li_(α)Co_(1-x-y)M_(y)Mn_(x)O_(δ)  (VII)

wherein 0.95≦α≦1.30, 0<x≦0.30, 0≦γ≦0.10, and 1.98≦δ≦2.04, and M is at least one element selected from the group consisting of B, Na, Mg, Ti, Ca, V, Cr, Fe, Co, Ni, Cu, Zn, Al, Sc, Y, Ga, Zr, Ru, and Mo. The compound of Formula (VII) is single phase. The compound can have a trigonal R3m crystal structure. In further variations, 0.98≦α≦1.16 and 0<x≦0.16. In some variations 0.98≦α≦1.16, 0<x≦0.16, 0≦γ≦0.05, 1.98≦δ≦2.04.

In some variations, the disclosure is directed to a compound represented by Formula (VIII):

Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ)  (VIII)

wherein 0.95≦α≦1.30, 0<x≦0.30, 0≦γ≦0.10, and 1.98≦δ≦2.04. In some variations, 0.96≦α≦1.04, 0<x≦0.10, 0≦γ≦0.10, and 1.98≦δ≦2.04. In some variations, the compounds represented by Formula (VIII) have 0.98≦α≦1.01, 0.02≦x≦0.04, 0≦γ≦0.03, and 1.98≦δ≦2.04. The compound of Formula (VIII) is a single phase. The compound can have trigonal R3m crystal structure.

In some instances, the compounds represented by Formulas (VII) and (VIII) have α>1+x. In other instances, α≦1+x. As such, α in Formulas (VII) and (VIII) can deviate from α=1+x, which may be associated with a solid-solution between Li₂MnO₃ and (1-x)LiCo_(1-y)M_(y)O₂. This solid solution can be represented by xLi₂MnO₃.(1-x)LiCo_(1-y)M_(y)O₂, and xLi₂MnO₃.(1-x)Li1-yCo_(1-y)M_(y)O₂, or in compact notation, Li_(1+x)Co_(1-x-y+xy)M_((1-x))*_(y)Mn_(x)O_(2+x) or Li_(1+x-y+xy)Co_(1−x-y+xy)M_((1-x))*_(y)Mn_(x)O_(2+x)

As described, the various compounds do not include a second phase, such as a second phase having a different crystal structure. It will be appreciated that Li₂MnO₃ is a “rock salt” phase having a monoclinic C2/m. crystal structure. Thus, cathode active materials based on the solid solution between Li₂MnO₃ and LiCo_(1-y)M_(y)O₂ have portions of “rock salt” phase that exhibit the monoclinic C2/m. crystal structure. This “rock salt” phase occurs in addition to any phases associated with LiCo_(1-y)M_(y)O₂, making the solid solution hi-phasic (or multi-phasic). In contrast, the cathode active materials represented by Formulas (VII) & (VIII), and variations thereof, are single phase and have only a trigonal R3m crystal structure.

Without wishing to be held to any particular mechanism or mode of action, manganese is incorporated into the compounds of Formulas (VII) and (VIII) to stabilize its R3m crystal structure, although other constituents of M may also contribute to stabilization. The compounds include a sub-lattice of Co in their R3m crystal structures in which Mn is uniformly distributed. Alternatively, in some variations, clusters of manganese (e.g., pairs, triplets, etc.) occur in the sub-lattice of Co that are uniformly distributed therein. Clustering can be detected, for example, by nuclear magnetic resonance (NMR) as described herein. The presence of Mn in the compounds may limit phase transitions from the R3m crystal structure during battery operation (e.g., charging, discharging, etc.). The presence of Mn may also improve an oxidative stability of the compound at higher voltages (e.g., voltages equal to or greater than 4.0V).

In some variations, x corresponds to a degree that Mn substitutes for Co. The degree of Mn substitution can correlate to the stability of compounds when used in cathode active materials. In various aspects, the substitution of Mn for Co can be greater than or equal to a lower substitution limit. Alternatively, the substitution of Mn for Co can be equal to or less than a substitution limit.

In some variations, x is at least 0.001. In some variations, x is at least 0.01. In some variations, x is at least 0.02. In some variations, x is at least 0.03. In some variations, x is at least 0.04. In some variations, x is at least 0.05. In some variations, x is at least 0.06. In some variations, x is at least 0.07. In some variations, x is at least 0.08. In some variations, x is at least 0.09. In some variations, x is at least 0.10. In some variations, x is at least 0.12. In some variations, x is at least 0.14. In some variations, x is at least 0.16. In some variations, x is at least 0.18. In some variations, x is at least 0.20. In some variations, x is at least 0.22. In some variations, x is at least 0.24. In some variations, x is at least 0.26. In some variations, x is at least 0.28.

In some variations, x is less than or equal to an upper substitution limit. In some variations, x is less than or equal to 0.30. In some variations, x is less than or equal to 0.28. In some variations, x is less than or equal to 0.26. In some variations, x is less than or equal to 0.24. In some variations, x is less than or equal to 0.22. In some variations, x is less than or equal to 0.20. In some variations, x is less than or equal to 0.18. In some variations, x is less than or equal to 0.16. In some variations, x is less than or equal to 0.14. In some variations, x is less than or equal to 0.12. In some variations, x is less than or equal to 0.10. In some variations, x is less than or equal to 0.09. In some variations, x is less than or equal to 0.08. In some variations, x is less than or equal to 0.07. In some variations, x is less than or equal to 0.06. In some variations, x is less than or equal to 0.05. In some variations, x is less than or equal to 0.04. In some variations, x is less than or equal to 0.03.

It will be understood that the lower and upper substitution limits may be combined in any variation as above to define a range for x, in any combination. For example, and without limitation, x may range from 0.001 to 0.01. x may range from 0.02 to 0.05 (i.e., 0.02≦x≦0.07). In another non-limiting example, x may range from 0.24 to 0.28 (i.e., 0.06≦x≦0.10). In still yet another non-limiting example, x may range from 0.24 to 0.28 (i.e., 0.2.2≦x≦0.28). Other combinations of the upper and lower limits are possible.

Furthermore, without wishing to be held to any particular mechanism or mode of action, a content of lithium may be selected in the compounds of Formulas (VII) and (VIII) to stabilize its R3m crystal structure and improve battery performance. The content of lithium may selectively complement a degree of substitution for Co (i.e., via Mn, M, or Al substitutions). For example, and without limitation, α may be selected to be about 1+x. Relative to α=1 this selection may improve stability of the R3m crystal structure during lithiation and de-lithiation (see FIG. 29). In another non-limiting example, α may be selected to be greater than 1+x to accommodate substitutes in addition to Mn (i.e., M and y). These substitutes may allow the compounds to have improved discharge energies (see FIG. 33), In still yet another example, the lithium content may be selected according to α≦1+x to enhance battery performance. As shown by FIG. 30, Li_(1.003)Co_(0.97)Mn_(0.03)O₂ maintains higher discharge energy after repeated cycling than Li_(1.014)Co_(0.97)Mn_(0.03)O₂, even though the latter has a higher value for a. In some variations, 0.98≦Li/Me≦1.01

It will be appreciated that a corresponds to a ratio of Li to Co and its substitutes (i.e., with reference to Formula (VII), M and Mn, and with reference to Formula (VIII), M, Mn, and Al). With respect to Formula (VII), the ratio can be depicted as [Li]i[Co_(1-x-y)M_(y)Mn_(x)]. With respect to Formula (VII), the ratio can be depicted as [Li]/[Co_(1-x-y)Al_(y)Mn_(x)]. For compounds with y=0, α corresponds to a ratio of Li to Co and Mn, i.e., [Li]/[Co_(1-x)Mn_(x)]. This latter ratio can be referred as the lithium to transition metal ratio (i.e., Li/TM).

In some variations, the compounds remain single phase and have the trigonal R3m crystal structure. In some variations, α can be equal to greater than a lower limit. In some variations, α is at least 0.95. In some variations, α is at least 0.98. In some variations, α is at least 1.00. In some variations, α is greater than 1.00. In some variations, α is at least 1.02. In some variations, α is at least 1.04. In some variations, α is at least 1.06. In some variations, α is at least 1.08. In some variations, α is at least 1.10. In some variations, α is at least 1.12. In some variations, α is at least 1.14. In some variations, α is at least 1.16. In some variations, α is at least 1.20. In some variations, α is at least 1.22. In some variations, α is at least 1.24. In some variations, α is at least 1.26. In some variations, α is at least 1.28.

Similarly, α can be less than or equal to a lower limit. In some variations, α is less than or equal to 1.30. In some variations, α is less than or equal to 1.28. In some variations, α is less than or equal to 1.26. In some variations, α is less than or equal to 1.24. In some variations, α is less than or equal to 1.22. In some variations, α is less than or equal to 1.20. In some variations, α is less than or equal to 1.16. In some variations, α is less than or equal to 1.14. In some variations, α is less than or equal to, 1.12. In some variations, α is less than or equal to 1.10. in some variations, α is less than or equal to 1.08. In some variations, α is less than or equal to 1.06. in some variations, α is less than or equal to 1.04. In some variations, α is less than or equal to 1.02. In some variations, α is less than or equal to 1.00. In some variations, α is less than 1.00. In some variations, α is less than or equal to 0.98. In these variations, the compounds also remain single phase and have the trigonal R3m crystal structure.

It will be understood that the lower and upper limits of α may be combined in any variation as above to define a range. For example, and without limitation, α may range from 0.95 to 1.00 (i.e., 0.95≦α≦1.00). In another non-limiting example, α may range from 1.00 to 1.06 (i.e., 1.00≦α≦1.08). In still yet another non-limiting example, α may range from 1.22 to 1.28 (i.e., 1.22≦α≦1.28). Other combinations of the upper and lower limits are possible.

It will also be understood that the lower and upper specification limits for x and the lower and upper limits for α may be combined in any variation as above to define combinations of ranges for x and α. For example, and without limitation, x≧0.03 and 0.98≦α≦1.10. In another non-limiting example, 0.02≦x≦0.10 and 0.95≦α≦1.12. In still yet another non-limiting example, 0.04≦x≦0.12 and 0.95≦α≦1.16. Other combinations of ranges are possible.

In some variations, α approaches 1+x. In these variations, α may approach 1+x within a tolerance not greater than 5%. The tolerance may correspond to (1−t)*(1+x)≦α≦(1+x)*(1+t) where t≦0.05. In some variations, the tolerance is less than or equal to ±5.0%. In some instances, the tolerance is less than or equal to ±14.5%. In some instances, the tolerance is less than or equal to ±4.0%. In some instances, the tolerance is less than or equal to ±3.5%. In some instances, the tolerance is less than or equal to ±3.0%. In some instances, the tolerance is less than or equal to ±2.5%. In some instances, the tolerance is less than or equal to ±2.0%. In some instances, the tolerance is less than or equal to ±1.5%. In some instances, the tolerance is less than or equal to ±1.0%.

In some instances, the tolerance is at least ±1.0%. In some instances, the tolerance is at least ±0.5%. In some instances, the tolerance is at least ±1.0%. In some instances, the tolerance is at least ±1.5%. %. In some instances, the tolerance is at least ±2.0%. In some instances, the tolerance is at least ±2.5%. In some variations, the tolerance is at least ±3.0%. In some instances, the tolerance is at least ±3.5%. In some instances, the tolerance is at least ±4.0%. In some instances, the tolerance is at least ±4.5%.

It will be understood that, when α approaches 1+x, the corresponding compounds maintain a single-phase character and do not have inclusions of Li₂MnO₃ therein. Moreover, the compounds can exhibit an improved resistance to phase transitions during charging and discharging, as well as improved discharge energies. Non-limiting examples of such compounds include Li_(1.050)Co_(0.96)Mn_(0.04)O₂, Li_(1.074)Co_(0.96)Mn_(0.04)O₂, Li_(1.197)Co_(0.78)Mn_(0.22)O₂, and Li_(1.247)Co_(0.72)Mn_(0.28)O₂.

In some variations, the compound is selected from among Li_(1.050)Co_(0.96)Mn_(0.04)O₂, Li_(1.074)Co_(0.96)Mn_(0.04)O₂, Li_(1.081)Co_(0.96)Mn_(0.04)O₂, Li_(1.089)Co_(0.96)Mn_(0.04)O₂, Li_(1.050)Co_(0.93)Mn_(0.07)O₂, Li_(1.065)Co_(0.90)Mn_(0.10)O₂, Li_(1.100)Co_(0.90)Mn_(0.10)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, Li_(1.158)CO_(0.90)Mn_(0.10)O₂, Li_(0.975)Co_(0.84)Mn_(0.16)O₂, Li_(1.050)Co_(0.84)Mn_(0.16)O₂, Li_(1.114)Co_(0.84)Mn_(0.16)O₂, Li_(1.197)Co_(0.78)Mn_(0.22)O₂, Li_(1.190)Co_(0.72)Mn_(0.28)O₂, and Li_(1.247)Co_(0.72)Mn_(0.28)O₂. In these compounds, manganese substitutes for cobalt without inducing the formation of Li₂MnO₃, i.e., the compounds are single phase and have the trigonal R3m crystal structure.

In some variations, the compound is Li_(0.991)Mn_(0.03)Co_(0.97)O₂. In some variations, the compound is Li_(0.985)Mn_(0.03)Co_(0.97)O₂.

The disclosure is further directed to powders comprising compounds described herein. In various aspects, the disclosure is directed to a powder that includes particles comprising any compound identified above. The powder may serve as part or all of a cathode active material (i.e., the cathode active material includes the powder).

The compounds and powders can be in a cathode active material for lithium ion batteries, as described herein. These cathode active materials assist energy storage by releasing and storing lithium ions during, respectively, charging and discharging of a lithium-ion battery.

Without wishing to be limited to a particular mechanism or mode of action, the compounds can improve volumetric energy density, energy retention, and/or cyclability of cathode active materials during charge and discharge of battery cells. The compounds can improve the thermal stability of the cathode active materials.

In some variations, the particles have a mean particle diameter greater than or equal to a first lower limit. In some variations, the particle has a mean diameter of at least 5 μm. In some variations, the particle has a mean diameter of at least 10 μm. In some variations, the particle has a mean diameter of at least 15 mm. In some variations, the particle has a mean diameter of at least 20 μm. In some variations, the particle has a mean diameter of at least 25 μm.

In some variations, the particles have a mean particle diameter less than or equal to a first upper limit. In some variations, the particle has a mean diameter of less than or equal to 30 μm. In some variations, the particle has a mean diameter of less than or equal to 25 μm. In some variations, the particle has a mean diameter of less than or equal to 20 μm. In some variations, the particle has a mean diameter of less than or equal to 15 μm. In some variations, the particle has a mean diameter of less than or equal to 10 μm. In some variations, the particle has a mean diameter of less than or equal to 5 μm.

It will be understood that the first lower and upper limits may be combined in any variation as above to define a first range for the mean particle diameter. For example, and without limitation, the mean particle diameter may range from 10 mm to 20 μm. In another non-limiting example, the mean particle diameter may range from 20 mm to 25 μm. Other ranges are possible. The particles having the aforementioned mean particle diameters, whether characterized by the first lower limit, the first upper limit, or both (i.e., the first range), may be processed according to a co-precipitation method.

In some variations, the particles have a mean particle diameter greater than or equal to a second lower limit. In some variations, the particle has a mean diameter of at least 200 nm. In some variations, the particle has a mean diameter of at least 300 nm. In some variations, the particle has a mean diameter of at least 400 nm. In some variations, the particle has a mean diameter of at least 500 nm. In some variations, the particle has a mean diameter of at least 600 nm. In some variations, the particle has a mean diameter of at least 700 nm.

In some variations, the particles have a mean particle diameter less than or equal to a second upper limit. In some variations, the particle has a mean diameter of less than or equal to 800 nm. In some variations, the particle has a mean diameter of less than or equal to 700 nm. In some variations, the particle has a mean diameter of less than or equal to 600 nm. In some variations, the particle has a mean diameter of less than or equal to 500 nm. In some variations, the particle has a mean diameter of less than or equal to 400 nm. In some variations, the particle has a mean diameter of less than or equal to 300 nm.

It will be understood that the second lower and upper limits may be combined in any variation as above to define a second range for the mean particle diameter. For example, and without limitation, the mean particle diameter may range from 300 nm to 500 nm. In another non-limiting example, the mean particle diameter may range from 400 nm to 800 nm. Other ranges are possible. The particles having the aforementioned mean particle diameters, whether characterized by the second lower limit, the second upper limit, or both (i.e., the second range), may be processed according to a sol-gel method.

In some variations, the particles are secondary particles are formed of agglomerated primary particles. The agglomerated primary particles may be sintered together. In some instances, the secondary particles have a mean particle diameter greater than or equal to a lower limit. Non-limiting examples of the lower limit include 15 μm, 20 μm, and 25 μm. In some instances, the secondary particles have a mean particle diameter less than or equal to an upper limit. Non-limiting examples of the upper limit include 30 μm, 25 μm, and 20 μm. It will be understood that the lower and upper limits may be combined in any variation as above to define a range for the mean particle diameter. For example, and without limitation, the mean particle diameter may range from 15 μm to 20 μm. In another non-limiting example, the mean particle diameter may range from 20 μm to 25 μm. Other ranges are possible.

In some variations, a single primary particle occupies a percentage of a volume occupied by a corresponding secondary particle. In some instances, the percentage is greater or equal to a lower limit. In some variations, a single primary particle occupies at least 30% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 35% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 40% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 45% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 50% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 55% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 60 of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies at least 65% of a volume occupied by a corresponding secondary particle.

In some variations, a single primary particle occupies less than or equal to 70% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 65% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 60% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 55% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 50% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 45% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 40% of a volume occupied by a corresponding secondary particle. In some variations, a single primary particle occupies less than or equal to 35% of a volume occupied by a corresponding secondary particle.

It will be understood that the lower and upper limits may be combined in any variation as above to define a range for the percentage. For example, and without limitation, the percentage may range from 30-50%. However, other ranges are possible.

As described herein, the larger particle sizes, and percentage of secondary particles occupied by a singled primary particle, can be formed by using higher sintering temperatures. Without wishing to be held to a particular mechanism or mode of action, in some instances the particles do not fracture as readily, and thereby can provide increased stability than conventional particles.

Including Mn and/or Al in the compound in place of Co, altering the amount of Li, and/or including an Al₂O₃ coating can reduce, or reduce the likelihood of, a destabilizing phase transition. Without wishing to be limited to a particular mechanism or mode of action, the additional elements also give greater oxidative stability to the compounds at higher battery upper cut-off voltages. In some variations, the compounds, particles, and/or cathode active materials can have increased stability for at least 4.4V vs. Li⁰/Li⁺.

In some variations, the particles have increased particle strength. The increased particle strength results in increased energy retention when the particles are used in a cathode active material.

In some variations, increased amount of manganese in cathode active materials provides for improved battery stability. In some variations, the increased amount of Mn increases the onset temperature of decomposition. In some variations, increased amounts of Mn can result in reduced amount of heat release at a decomposition temperature of the compound.

In some variations, the cathode active materials have a first-cycle discharge energy of at least 700 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 725 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 750 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 775 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 800 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at, least, 825 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 850 Wh/kg. In some variations, the cathode active materials have a first-cycle discharge energy of at least 875 Wh/kg.

In some variations, the cathode active materials have a first-cycle discharge capacity of at least 180 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 185 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 190 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 195 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 200 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 205 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 210 mAh/g. In some variations, the cathode active materials have a first-cycle discharge capacity of at least 215 mAh/g.

In some variations, the cathode active materials have an energy capacity retention of at least 65% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 67% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 69% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 71% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 73% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 75% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 77% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 79% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 81% after 52 charge-discharge cycles. In some variations, the cathode active materials have an energy capacity retention of at least 83% after 52 charge-discharge cycles.

The compounds, powders, and cathode active materials can be used in batteries as described herein. The materials can be used in electronic devices. An electronic device herein can refer to any electronic device known in the art, including a portable electronic device. For example, the electronic device can be a telephone, such as a cell phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone®, an electronic email sending/receiving device. The electronic device can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. The electronic device can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), watch (e.g., AppleWatch), or a computer monitor. The electronic device can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV®), or it can be a remote control for an electronic device. Moreover, the electronic device can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The battery and battery packs can also be applied to a device such as a watch or a clock. The components powered by a battery or battery pack can include, but are not limited to, microprocessors, computer readable storage media, in-put and/or out-put devices such as a keyboard, track pad, touch-screen, mouse, speaker, and the like.

EXAMPLES

The following examples are for illustration purposes only. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the disclosure.

Example 1—Wet Impregnation to Form an Al₂O₃ Coating

De-ionized water (Millipore ultra-pure water, 18 MΩ·cm) was added drop-wise to 10 g of base powder (i.e., 10 g of Li_(1.04)Co_(0.96)Mn_(0.04)O_(2.04) base powder) while stirring. When the powder was wetted yet still loose, the stirring was stopped. (The addition of de-ionized water was stopped before the powder formed a watery or sticky mass.) A ratio, R, was then calculated that equaled an amount (either weight or volume) of added water divided by an amount of base powder. The amount of water needed to wet the powder to a suitable dampness depends on the surface area of the base powder used. In general, higher surface areas require more water.

Next, a quantity (e.g., weight) of base powder was selected. An amount of aluminum salt precursor (e.g., aluminum nitrate nonahydrate) was determined that would correspond to a desired level of Al₂O₃ coating on the desired quantity base powder (e.g., 0.1 wt. %). An amount of de-ionized water was then calculated using the ratio (i.e., multiplying R times the weight of the base powder). TABLE 1 presents types and quantities of base powder, solvent (i.e., de-ionized water), and aluminum salt precursor.

The quantities given in TABLE 1 were then measured, including the de-ionized water whose amount was predetermined. Aluminum nitrate nonahydrate was dissolved in the de-ionized water to form a clear solution. Drops of the clear solution were added to the base powder in a glass container under stirring. Once the clear solution was consumed, the base powder was stirred continuously for a few minutes to ensure well-mixing. A wetted, loose powder was formed.

The wetted, loose powder was dried in an oven overnight at 80° C. The dried powder was then transferred to an Al₂O₃ crucible and heat-treated at 120° C. for 2 hours. This heat treatment was followed by a subsequent heat treatment at 500° C. for 4 hours in stagnant air. The heat-treated powder was passed through 325-mesh sieve. Occasionally, light grinding with mortar and pestle was needed to break up agglomerated portions of the heated-treated powder.

TABLE 1 Materials for 0.1 wt. % Al₂O₃ Coating on 10 g Li_(1.04)Co_(0.96)Mn_(0.04)O₂ Material Reagent/Material Quantity Used Base powder Li_(1.04)Co_(0.96)Mn_(0.04)O₂ 10 g Solvent (for dissolving De-ionized water ~0.9-1 ml or g coating precursor) Coating Precursor Al(NO₃)₃•9H₂O 0.075 g

Example 2—Wet Impregnation to Form an AlF₃ Coating

A ratio, R, was determined according to procedures described in relation to Example 1.

Next, a quantity (e.g., weight) of base powder was selected. An amount of aluminum salt precursor (e.g., aluminum nitrate nonahydrate) and fluoride salt precursor (e.g., ammonium fluoride) was determined that would correspond to a level of AlF₃ coating on the desired quantity base powder (e.g., 0.1 wt. %). To ensure complete reaction, the amount of fluoride salt precursor was doubled relative to a stoichiometric amount of fluoride in AlF₃ (i.e., a mole ratio of Al to F was selected to be 1:6). A needed amount of de-ionized water was then calculated using the ratio (i.e., multiplying R times the weight of the base powder).

Aluminum nitrate nonahydrate was dissolved in a first portion of the de-ionized water to form a first clear solution. Ammonium fluoride was dissolved in a second portion of de-ionized water to form a second clear solution. The base powder was transferred to a glass container and drops of the first clear solution were added quickly therein (i.e., to “flood” the base powder). The base powder was stirred for 2 minutes and the dried at 105° C. to yield a powder cake.

The powder cake was broken up into a loose powder (e.g., with a mortar and pestle) and then transferred into a fresh glass container. The fresh glass container was gently tapped to pack the loose powder therein. The second clear solution was quickly added to the packed powder while stirring (i.e., similar to the first clear solution). This mixture was stirred for 2 minutes before drying at 105° C. The dried powder was transferred to an alumina saggar for heat treatment for 2 hours at 120° C. in flowing nitrogen. The heat-treated powder was then heated at 400° C. for 5 hours, resulting in a heat-treated powder cake. The heat-treated powder cake readily broke apart and was lightly ground and sieved through a 325 mesh.

Example 3—Wet Impregnation to Form an AlPO₄ Coating

A predetermined amount of base powder (i.e., Li_(1.04)Co_(0.96)Mn_(0.04)O₂) was weighed out in a glass container. An amount of aluminum and phosphate precursor needed for a desired amount of AlPO₄ coating (e.g., 5 wt. %) was calculated based on the weighed amount of base powder. The aluminum precursor used included various aluminum salts such as aluminum nitrate, aluminum acetate, or other aluminum salt soluble in water or alcohol. The phosphate precursor used was either ammonium dihydrogen phosphate (NH₄H₂PO₄), diammonium hydrogen phosphate [(NH₄)₂HPO₄], or a combination of both. A mole ratio of Al to P was kept between 0.9 and 1.1. The aluminum precursor and phosphate precursor were dissolved separately in a small amount of water or alcohol to form solutions. The two solutions were then mixed together. The pH of the mixed solution was adjusted by varying a ratio of the ammonium phosphate salts to prevent precipitation. The mixed solution was added drop-wise onto the base powder while stirring with a glass rod or spatula. The volume of solution was such that the base powder was incipiently wet and well mixed (i.e., exhibited a damp consistency). After drying at 50-80° C., the dried base powder was heat-treated at 700° C. for 5 h in stagnant air.

Example 4—Wet Impregnation to Form a Co₃(PO₄)₂ Coating

A predetermined amount of base powder (i.e., Li_(1.04)Co_(0.96)Mn_(0.04)O₂) was weighed out in a glass container. An amount of cobalt and phosphate precursor needed for a desired amount of Co₃(PO₄)₂ coating (e.g., 5 wt. %) was calculated based on the weighed amount of base powder. The cobalt precursor used included various cobalt salts such as cobalt nitrate, cobalt acetate, or other cobalt salt soluble in water or alcohol. The phosphate precursor used was either ammonium dihydrogen phosphate (NH₄H₂PO₄), diammonium hydrogen phosphate [(NH₄)₂HPO₄], or a combination of both. A mole ratio of Co to P was kept between 1.4 and 1.6. The cobalt precursor and the phosphate precursor were dissolved separately in a small amount of water or alcohol to form solutions. The two solutions were then mixed together. A pH of the mixed solution was adjusted by varying a ratio of the ammonium phosphate salts to prevent precipitation. The mixed solution was added drop-wise onto the base powder while stirring with a glass rod or spatula. The volume of solution added was such that the base powder was incipiently wet and well mixed (i.e., exhibited a damp consistency). After drying at 50-80° C., the dried base powder was then heat-treated at 700° C. for 5 h in stagnant air.

Example 5—Wet Impregnation to Form a Li—Al₂O₃ Coating

A predetermined amount of base powder (i.e., Li_(1.04)Co_(0.96)Mn_(0.04)O₂) was weighed out into a glass beaker. An amount of aluminum precursor needed for the desired amount of coating (e.g., 0.5 wt. %) was calculated based on the weighed amount of base powder. The aluminum precursor included various aluminum salts such as aluminum nitrate, aluminum acetate, or other aluminum salts soluble in water or alcohol. The aluminum precursor was dissolved in a small amount of water or alcohol to form a first clear solution. A desired amount of lithium precursor was calculated using a molar ratio of Li to Al between 0.25 and 1.05. The lithium precursor used was lithium hydroxide, lithium nitrate, lithium acetate, or other lithium salts soluble in water or alcohol. The desired amount of lithium precursor was dissolved in a small amount of water or alcohol to form a second clear solution. The first and second clear solutions were mixed together. This mixed solution was then added drop-wise to the base powder while stirring. The volume of solution added was such that the base powder became incipiently wet but not watery (i.e., exhibited a damp consistency). After drying at 50-80° C., the dried base powder was then heat-treated to 500° C. for 4 h in stagnant air. The pH of the first clear solution (i.e., the aluminum solution) can also be varied to improve coating properties such as coating density and uniformity.

Example 6—Wet Impregnation to Form a Li—Co₃(PO₄)₂ Coating

A predetermined amount of base powder (i.e., Li_(1.04)Co_(0.96)Mn_(0.04)O₂) was weighed out into a glass beaker. An amount of cobalt, phosphate, and lithium precursors needed for a desired amount of coating (e.g., 0.5 wt. %) was calculated based on the weighed amount of base powder. The cobalt precursor included various cobalt salts such as cobalt nitrate, cobalt acetate, or other cobalt salts soluble in water or alcohol. The phosphate precursor used was either ammonium dihydrogen phosphate (NH₄H₂PO₄), diammonium hydrogen phosphate [(NH₄)₂HPO₄], lithium phosphates, or combinations of such. A mole ratio of Co to P is kept between 1.4 and 1.6. A desired amount of lithium precursor was calculated using a molar ratio of Li to Co between 0.3 and 1.05. The lithium precursor used was lithium hydroxide, lithium nitrate, lithium acetate, or other lithium salts soluble in water or alcohol. The cobalt, phosphate and lithium precursors were dissolved separately in a small amount of water or alcohol to form corresponding clear solutions. The three solutions were then mixed together. This mixed solution was then added drop-wise to the base powder while stirring. The volume of solution added was such that the base powder became incipiently wet but not watery (i.e., exhibited a damp consistency). After drying at 50-80° C., the dried base powder was heat-treated to 700° C. for 5 h in stagnant air.

Example 7—Suspension Processing to Form an Al₂O₃ Coating

An aqueous solution of Al(NO₃)₃ was mixed with a suspension of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) and then pumped into a stirred-tank reactor. While stirring, an ammonia solution was used to hold a reaction pH value at 9.3 using a feedback pump. The suspension was stirred for 2 h, filtered, dried, and calcined at 400° C. for 5 h in air.

Example 8—Suspension Processing to Form a Co₃(PO₄)₂ Coating

A first aqueous solution of Co(NO₃)₃ and a second aqueous solution of ammonium dihydrogen solution were pumped into a suspension of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) in a stirred-tank reactor. The combined volume was stirred for 2 h, filtered, and dried. The dried powder was calcined at 700° C. for 5 h in air.

Example 9—Suspension Processing to Form an AlPO₄ Coating

A first aqueous solution of Al(NO₃)₃ and a second solution of ammonium dihydrogen phosphate were pumped into a suspension of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) in a stirred-tank reactor. The combined volume was stirred for 2 h, filtered, and dried. The dried powder was calcined at 700° C. for 5 h in air.

Example 10—Dry Processing to Form an Al₂O₃ Coating

A predetermined amount of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) was weighed out and poured into a dry coater (Nobilta, NOB-130, Hosokawa Micron Ltd). Next, nanocrystalline Al₂O₃ powder was weighed out according to a desired amount of coating on the predetermined base powder (e.g., 0.5 wt. %). The weighed nanocrystalline Al₂O₃ powder was poured into the dry coater. The dry coater included a high speed rotary mixer that bonds, via a mechanofusion process, particles of the nanocrystalline Al₂O₃ powder to particles in the base powder (i.e., along a surface thereof). For a 0.5 wt. % coating, 2.5 g of nanocrystalline Al₂O₃ powder was mixed thoroughly with 500 g of base powder. The speed was controlled at 4000 rpm. After 5 min, an Al₂O₃-coated base powder was formed.

Example 11—Dry Processing to Form an AlF₃ Coating

A predetermined amount of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) was weighed out and poured into a dry coater (Nobilta, NOB-130, Hosokawa Micron Ltd). Next, nanocrystalline AlF₃ powder was weighed out according to a desired amount of coating on the predetermined base powder (e.g., 0.1 wt. %). The weighed nanocrystalline AlF₃ powder was poured into the dry coater. For a 0.1 wt. % coating, 0.5 g of AlF₃ was mixed thoroughly with 500 g of base powder. The speed was controlled at 4000 rpm. After 5 min, an AlF₃-coated base powder was formed.

Example 12—Dry Processing to Form a Coating of Al₂O₃ and AlF₃

A predetermined amount of base powder (Li_(1.02)Co_(0.96)Mn_(0.04)O₂) was weighed out and poured into a dry coater (Nobilta, NOB-130, Hosokawa Micron Ltd). Next, nanocrystalline Al₂O₃ powder and nanocrystalline AlF₃ powder were weighed out according to a desired amount of coating on the predetermined base powder (e.g., 0.1 wt. %). The weighed nanocrystalline powders were poured into the dry coater. For a 0.1 wt. % coating, 0.25 g of Al₂O₃ and 0.05 g of AlF₃ were mixed thoroughly with 500 g of base powder. The speed was controlled at 4000 rpm. After 5 min, a base powder coated with Al₂O₃ and AlF₃ was formed.

Example 13—Powder Characterization

The morphology, composition, and electrochemical performance of certain coated powders were evaluated with scanning electron microscopy (SEM), inductively-coupled plasma optical emission spectroscopy (ICP-OES), and a Maccor tester.

FIGS. 3A-3C present a series of scanning electron micrographs showing, respectively, a base powder, a 0.1 wt. % AlF₃-coated base powder, and a 0.1 wt. % Al₂O₃-coated base powder, according to an illustrative embodiment. The base powder corresponds to particles comprising Li_(1.02)Co_(0.96)Mn_(0.04)O₂. Only a subtle difference is shown for the powders before and after wet impregnation. Compared to an uncoated powder, i.e., FIG. 3A, surfaces of the coated powders appear furry and rough as indicated by stains or bumps, i.e., FIGS. 3B and 3C.

Quantities of Al₂O₃ and AlF₃ coated on base powder samples were determined with ICP-OES. TABLES 2 and 3 show the results for, respectively, Al₂O₃ and AlF₃ wet-impregnated base powders. A comparison of target coating levels with measured values indicates that the measured values match very well with their corresponding target values for coating levels ≧0.2 wt. %.

TABLE 2 ICP-OES results of Al₂O₃-coated and uncoated base powders Li/(Co + Mn/(Co + Al/(Co + Co/(Co + Mn + Ni) Mn + Ni) Mn + Ni) Mn + Ni) Sample No. Target Al2O3, wt % Measured Al2O3 Value ± Value ± Value ± Value ± XW189a 0.05 0.0775 0.989 0.002 0.0396 0.0001 0.0018 0.0001 0.96 3E−04 XW189b 0.1 0.1323 0.988 0.002 0.0396 0.0001 0.0028 0.0002 0.96 3E−04 XW189c 0.5 0.5083 0.988 0.002 0.0396 9E−05 0.0102 0.0006 0.959 4E−04 XW190a 0.5 0.4648 0.987 0.002 0.0395 8E−05 0.0095 0.0008 0.959 6E−04 Uncoated 0 1.008 0.002 0.0397 0.0001 0.003 0.0002 0.96 3E−04 HW168

TABLE 3 ICP-OES results of AlF₃-coated and uncoated base powders Li/(Co + Mn/(Co + Al/(Co + Co/(Co + Mn + Ni) Mn + Ni) Mn + Ni) Mn + Ni) Sample No. Target coating, wt % Measured AlF3, wt % Value ± Value ± Value ± Value ± CL130a 0.05 0.103 0.9877 0.002 0.03955 0.00012 0.00145 0.00011 0.9597 0.0003 CL129b 0.1 0.156 0.9871 0.002 0.03956 0.00012 0.00205 0.00016 0.9601 0.0003 CL125 0.2 0.224 0.9867 0.0021 0.03953 0.00008 0.00307 0.00025 0.9595 0.0006 CL129a 0.2 0.221 0.9853 0.0021 0.03951 0.00008 0.00304 0.00025 0.9595 0.0006 Uncoated 0 1.0083 0.0021 0.03965 0.00012 0.00301 0.00023 0.9596 0.0003 HW168

Example 14

Electrochemical tests were conducted on 2032 coin half-cells having a cathode active material loading of approximately 15 mg/cm². An electrolyte used by the 2032 coin half-cells included 1.2 M LiPF₆ in an EC:EMC solvent of 3:7 ratio by weight. The cells were placed on a Maccor Series 2000 tester and cycled in galvanostatic mode at room temperature with the voltage windows of 4.5V to 2.75V. A series of electrochemical tests of formation, rate, and cycling were conducted under each voltage window. During formation testing, a constant current (0.2C) was applied to the cell during the charge process, followed by a constant voltage charge until the current was equal to or less than 0.05C. Then, the cells were discharged at constant current (0.2C) until the end of discharge. Charging and discharging of the cells were repeated three times. During rate testing, the charging rate was fixed to 0.7C for all the rate tests, and then followed by constant voltage charge until the current was equal to or less than 0.05C. Five different discharge rates of 0.1C, 0.2C, 0.5C, 1C, and 2C were applied until the cells were completely discharged. Three cycles were conducted for each rate. Finally, 50 cycles were conducted to investigate cycle life. The same charging conditions as those of the rate test were applied. The discharge rate was fixed to 0.5C for all the cycles.

Here we present the cycle data for the base powder Li_(1.04)Co_(0.96)Mn_(0.04)O₂ and the two highest performing coated samples (Li_(1.04)Co_(0.96)Mn_(0.04)O₂—Al₂O₃ 0.05 wt % and Li_(1.04)Co_(0.96)Mn_(0.04)O₂—AlF₃ 0.1 wt %).

FIG. 4 presents a plot of data representing a performance of three coin half-cells, each incorporating a single cathode active material, during a first cycle of charging and discharging, according to an illustrative embodiment. The single cathode active material for each of three coin half-cells corresponds to, respectively, the base powder Li_(1.04)Co_(0.96)Mn_(0.04)O₂ (i.e. “HW168”), 0.05 wt. % Al₂O₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂, (i.e., “HW168-Al₂O₃ 0.05 wt. %) and 0.1 wt. % AlF₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ (i.e., “HW168-AlF₃ 0.1 wt. %). The performance of the three coin half-cells is characterized by two bars: A leftmost bar indicates a first cycle charge capacity and a rightmost bar indicates a first cycle discharge capacity.

In FIG. 4, the presence of coatings in the cathode active material slightly reduces the first cycle charge capacity and discharge capacity as both the Al₂O₃- and AlF₃-coated variants show a 4 mAh/g reduced capacity relative to the uncoated variant. This value is higher than what was expected for such small amount of coating. Such reduction in capacity may be attributed to the loss of lithium during the coating process, as indicated by the ICP-OES data in TABLES 3 and 4. However, the performance shown by FIG. 4, which is an initial performance, is not representative of coin half-cell performance in subsequent charge and discharge cycles.

FIGS. 5 and 6 present a plot of data representing a change in capacity, over extended cycling, of the three coin half-cells of FIG. 4, according to an illustrative embodiment. FIGS. 7 and 26 present a plot of data representing a change in energy density, over extended cycling, of the three coin half-cells of FIG. 4, according to an illustrative embodiment. FIGS. 5 and 7 correspond to rate testing and FIGS. 6 and 8 correspond to life testing.

FIG. 5 shows that, up to a 1C rate, the presence of coatings did not affect the performance of coin half-cells incorporating Li_(1.04)Co_(0.96)Mn_(0.04)O₂, Al₂O₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂, and AlF₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂. Their capacities are similar up to a 1C rate (i.e., for C/10, C/5, C/2, and 1C). The coin half-cell corresponding to Al₂O₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ showed a reduced (relative) performance at a 2C rate.

Coating benefits are more clearly highlighted in FIG. 6, which presents life testing. Coin half-cells corresponding to coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ variants show improved capacities relative to uncoated Li_(1.04)Co_(0.96)Mn_(0.04)O₂. the coin half-cells associated with coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ lose only 4-5 mAh/g.

The coin half-cell incorporating uncoated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ started with lower capacity, i.e., relative to those incorporating coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂, because this cell half-cell was already cycled 19 times after the aging and the rate tests. Such pre-aging resulted in quicker degradation than those not pre-aged (i.e., those utilizing coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂). More than 15 mAh/g of capacity was lost over a 26 life cycle test.

A similar trend was observed in FIGS. 7 and 8 for energy density as described in relation to FIGS. 5 and 6. However, the coin half-cell associated with uncoated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ starts at a lower energy density than those the two coated sample (FIGS. 7 and 8). The AlF₃-coated samples maintain a higher energy density than the Al₂O₃-coated sample.

FIGS. 9 and 10 present plots of data representing to charge-discharge profiles for each the three coin half-cells of FIG. 4. FIG. 9 presents rate testing and FIG. 10 presents life testing. These profiles demonstrate an advantage of the coatings disclosed herein. The shape of curves was more preserved for coin half-cells incorporating Al₂O₃- and AlF₃-coated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ than those base powder Li_(1.04)Co_(0.96)Mn_(0.04)O₂. Indeed, the variant corresponding to uncoated Li_(1.04)Co_(0.96)Mn_(0.04)O₂ shows the fastest decay in capacity with increasing cycle number.

FIGS. 11 and 12 present plots of data representing dQ/dV profiles for each the three coin half-cells of FIG. 4. FIG. 11 presents rate testing and FIG. 12 presents life testing. Curves in each profile were plotted every 5 cycles for both rate and life tests. A reduction peak at approximately 3.85V characterizes a structural stability of the cathode active material in each coin half-cell during progressive cycling.

A degradation of the cathode active material (i.e., structural instability) is reflected by shifting and broadening of the reduction peak toward lower voltages. During rate testing, the coin half-cell corresponding to base powder Li_(1.04)Co_(0.96)Mn_(0.04)O₂ showed the highest degradation with a relatively fast shift away from 3.85V and a large peak broadening. In contrast, the coin half-cells corresponding to its coated variants showed slower shifts and weaker broadening. Peak shifting and broadening are less evident during rate testing than life testing. This behavior results from lower amounts of lithium ions being cycled back and forth as a charge/discharge rate progressively increases. During the life test, the coin half-cell incorporating baseline LiCoO₂ showed further degradation while those incorporating Li_(1.04)Co_(0.96)Mn_(0.04)O₂ and its coated variants showed almost no degradation.

Example 15—Cathode Active Materials by Co-Precipitation Methods

A 3.5-liter stirred tank reactor was filled with distilled water and heated to 60° C. A flow of nitrogen gas was introduced into the tank reactor while stirring the distilled water at a rate of 1100 rpm. Separately, manganese and cobalt sulfate were dissolved in distilled water to produce a first aqueous solution having a total concentration of 2.0M and a predetermined molar ratio (i.e., [Mn]:[Co]). The ratio included representative examples, such as [Mn][Co], 0.00:1.00, 0.04:0.96, 0.07:0.93, 0.10:0.90, 0.16:0.84, and 0.28:0.72. The first aqueous solution was continuously dripped into distilled water of the tank reactor at a flow rate of 100 ml/h to produce a combined aqueous solution. The pH of the combined aqueous solution was fixed at 11.5 by adding a second aqueous solution of sodium hydroxide and ammonia using a pH controller coupled to a. pump. Over a 300 hour run-time, particles nucleated and grew in the combined aqueous solution, thereby forming final precursor particles. The final precursor particles were washed, filtered, and dried at 175° C. for 12 h.

The final precursor particles were used to form cathode active materials of composition LiMn_(x)Co_(1-x)O₂ where x and 1-x correspond to the predetermined molar ratio, i.e., [Mn]:[Co]=[x][1-x]. A solid-state reaction was carried out with Li₂CO₃ powder and powders of the final precursor particles. The molar ratio of Li₂CO₃ and the final precursor particles with was varied to yield cathode active materials having variations in ratios of [Li]:[Mn_(x)Co_(1-x)] (i.e., ratios of lithium to total transition-metal content). The Li₂Co₃ powder and powders of the final precursor particles were blended in an orbital mixer to produce a mixed powder. Following blending, the mixed powder was transferred to an alumina tray and heated in flowing air at 700° C. for 10 hours. The ramp rate of the furnace was 5° C. per minute. After heating at 700° C., the mixed powder, now reacted, was allowed to cool in the furnace to ambient temperature via natural heat losses. The resulting intermediate powder was ground by mortar and pestle, sieved, and re-fired at 1050° C. in flowing air for 15 hours. The ramp rate was 5° C. per minute, and after firing, the resulting sintered powder was allowed to cool in the furnace to ambient temperature via natural heat losses. The sintered powder was broken up, ground by mortar and pestle, and sieved to produce a cathode active material. Samples of the cathode active materials were characterized by powder X-ray diffraction using a Bruker D8 (see FIGS. 20 and 21).

Representative examples of cathode active materials prepared by the above-described co-precipitation method include LiCoO₂, Li_(0.987)CO_(0.96)Mn_(0.04)O₂, Li_(1.050)CO_(0.96)Mn_(0.04)O₂, Li_(1.074)Co_(0.96)Mn_(0.04)O₂, Li_(1.081)Co_(0.96)Mn_(0.04)O₂, Li_(1.089)Co_(0.96)Mn_(0.04)O₂, Li_(0.981)Co_(0.93)Mn_(0.07)O₂, Li_(1.050)CO_(0.93)Mn_(0.07)O₂, Li_(0.984)Co_(0.90)Mn_(0.10)O₂, Li_(1.065)Co_(0.90)Mn_(0.10)O₂, Li_(1.1000)Co_(0.90)Mn_(0.10)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, Li_(1.158)Co_(0.90)Mn_(0.10)O₂, Li_(0.975)Co_(0.84)Mn_(0.16)O₂, Li_(1.050)Co_(0.84)Mn_(0.16)O₂, Li_(1.114)Co_(0.84)Mn_(0.16)O₂, Li_(0.994)Co_(0.78)Mn_(0.22)O₂, Li_(1.100)Co_(0.78)Mn_(0.22)O₂, Li_(1.197)Co_(0.78)Mn_(0.22)O₂, Li_(0.973)Co_(0.72)Mn_(0.28)O₂, Li_(1.087)Co_(0.72)Mn_(0.28)O₂, Li_(1.190)Co_(0.72)Mn_(0.28)O₂, and Li_(1.247)Co_(0.72)Mn_(0.28)O₂.

FIG. 19 presents scanning electron micrographs of cathode active materials prepared according to the co-precipitation method described above. The micrographs indicate secondary particles formed of densely-sintered primary particles. Such densely-sintered secondary particles are typical for cathode active materials prepared by the co-precipitation method. The compositions of the cathode active materials correspond to Li_(0.96)Co_(0.93) Mn_(0.07) O₂, Li_(0.98)Co_(0.93) Mn_(0.07) O₂, and Li_(1.00)Co_(0.93) Mn_(0.07)O₂.

FIG. 20 presents X-ray powder diffraction patterns for cathode active materials represented by compositions of Li_(1.074)Co_(0.96)Mn_(0.04)O₂, Li_(1.081)Co_(0.96)Mn_(0.04)O₂, Li_(1.089)Co_(0.96) Mn_(0.04)O₂, Li_(1.065)Co_(0.90)Mn_(0.10)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, Li_(1.158)Co_(0.90) Mn_(0.10)O₂, Li_(0.975)Co_(0.84) Mn_(0.16)O₂, Li_(1.050)Co_(0.84)Mn_(0.16)O₂, and Li_(1.114)Co_(0.84)Mn_(0.16)O₂. These cathode active materials were prepared according to the co-precipitation method described above. In FIG. 20, groups of diffraction patterns are arranged from bottom to top that correspond, respectively, to increasing manganese content, i.e., from 0.04 to 0.10 to 0.16. Within each group, however, the lithium to transition-metal ratio (i.e., [Li]/[MnCo_(1-x)]) decreases in three increments from bottom to top. Reference bars indicating the peaks expected for Li₂MnO₃, Co₃O₄, and LiMnO₂, are shown in pink, grey, and blue colors, respectively.

The cathode active materials in FIG. 20 are mostly single phase. The absence of peaks in the vicinity of 2θ=20° indicates the absence of Li₂MnO₃ in the cathode active materials. Moreover, despite increasing substitution of Mn for Co, the crystal structure of each cathode active material, as represented by space group, remains at R3m. However, for low values of [Li]/[Mn_(x)Co_(1-x)], i.e., Li_(0.975)Co_(0.84)Mn_(0.16)O₂, metal-oxide phases of M₃O₄ stoichiometry emerge (e.g., Co₃O₄).

FIG. 21 presents X-ray powder diffraction patterns for cathode active materials represented by compositions of Li_(0.994)Co_(0.78)Mn_(0.22)O₂, Li_(1.100)Co_(0.78)Mn_(0.22)O₂, Li_(1.197)Co_(0.78)Mn_(0.22)O₂, Li_(0.973)Co_(0.72)Mn_(0.28)O₂, Li_(1.087)Co_(0.72)Mn_(0.28)O₂, Li_(1.19)Co_(0.72)Mn_(0.28)O₂, and Li_(1.24) O_(0.72)Mn_(0.28)O₂. These cathode active materials were prepared according to the co-precipitation method described above. In FIG. 3, groups of diffraction patterns are arranged from bottom to top that correspond, respectively, to increasing manganese content, i.e., 0.22 and 0.26. Within each group, however, the lithium to transition-metal ratio (i.e., [Li]/[Mn_(x)Co_(1-x)]) decreases in three increments from bottom to top. Reference bars indicating the peaks expected for Li₂MnO₃ and Co₃O₄ are shown.

In FIG. 21, the substitution of Mn for Co is higher in than that in FIG. 20. However, the crystal structure of each cathode active material, as represented by space group, is R3m. Diffraction patterns for Li_(0.994)Co_(0.78)Mn_(0.22)O₂, Li_(1.10)Co_(0.78)Mn_(0.22)O₂, Li_(0.973)Co_(0.72)Mn_(0.28)O₂, and Li_(1.087)Co_(0.72)Mn_(0.28)O₂ show peaks in the vicinity of 2θ=20°. Such peaks indicate the presence of small proportions of Li₂MnO₃ in these cathode active materials. However, the peaks are not present in cathode active materials represented by compositions with values of [Li]/[Mn_(x)Co_(1-x)] approaching. 1+x, i.e., Li_(1.197)Co_(0.78) Mn_(0.22)O₂ and Li_(1.247)Co_(0.72)Mn_(0.28)O₂. These latter cathode active materials are single phase. The metric 1+x corresponds to an ideal solid-solution stoichiometry for xLi₂MnO₃.(1-x)LiCoO₂ (i.e., Li_(1+x)Co_(1−x)Mn_(x)O_(2+x)).

Example 16—Cathode Active Materials by Sol-Gel Methods

A first aqueous solution of manganese acetate and cobalt acetate was prepared at a predetermined molar ratio (i.e., [Mn]:[Co]) and a total of 2 mol. As described below, the predetermined ratio included representative examples such as [Mn]:[Co]=0.10:0.90, 0.16:0.84, 0.22:0.78, and 0.28:0.72. A second aqueous solution of 1.0 M citric acid was added to the first aqueous solution and mixed via magnetic stirring to produce a combined solution. The combined solution was heated to 80° C. to form a gel, which was subsequently kept at 80° C. for 6 hours. The gel was then transferred into a box furnace and calcined at 350° C. for 4 hours. After cooling, the resulting cake was ground by mortar and pestle, sieved, and re-fired at 900° C. in flowing air for 12 hours. The ramp rate was 5° C. per minute, and after firing, the resulting cathode active material was allowed to cool in the furnace to ambient temperature via natural heat losses. Samples of the cathode active materials were characterized by powder X-ray diffraction using a Bruker D8 (see FIG. 23).

Representative examples of cathode active materials produced by the above-described sol-gel method include Li_(1.131)Co_(0.90)Mn_(0.10)O₂, Li_(1.198)Co_(0.84)Mn_(0.16)O₂, Li_(1.241)Co_(0.78)Mn_(0.22)O₂, and Li_(1.301)Co_(0.72)Mn_(0.28)O₂.

FIG. 22 presents scanning electron micrographs of cathode active materials prepared according to the sol-gel method described above. The micrographs indicate sheet-like agglomerations of fine particles having dimensions less than 1 μm. Such fine particle morphology is typical for cathode active materials prepared by the sol-gel method. The compositions of the cathode active materials correspond to Li_(1.1)Co_(0.1)Al_(0.01)Mg_(0.01)Mn_(0.89)O₂ and is Li_(1.28)Co_(0.258)Al_(0.02)Mg_(0.02)Co_(0.68)O₂.

FIG. 23 presents X-ray powder diffraction patterns for cathode active materials represented by compositions of Li_(1.131)Co_(0.90)Mn_(0.10)O₂, Li_(1.198)Co_(0.84)Mn_(0.16)O₂, Li_(1.241)Co_(0.78)Mn_(0.22)O₂, and Li_(1.301)Co_(0.72)Mn_(0.28)O₂. These cathode active materials were prepared according to the sol-gel method described above. The cathode active materials are single-phase. The crystal structure of each cathode active material, as represented by space group, is R3m. The absence of peaks in the vicinity of 2θ=20° indicates the absence of Li₂MnO₃ in these cathode active materials. Moreover, peak splitting in the vicinity of 2θ=65° indicates a well-crystallized layered structure.

Example 17—Battery Performance

FIG. 24 presents differential capacity curves for cathode active materials represented by compositions of LiCoO₂, Li_(1.05)Co_(0.96)Mn_(0.04)O₂, Li_(1.05)Co_(0.93)Mn_(0.07)O₂, Li_(1.110)Co_(0.90)M_(0.10)O₂, and Li_(1.19)Co_(0.72)Mn_(0.28)O₂. These cathode active materials were prepared according to the co-precipitation method described above. Measurements of differential capacity were taken of 2032 coin half-cells during a first-cycle charge and discharge at a rate of C/5, In FIG. 24, the ordinate indicates magnitudes of dQ/dV and the abscissa indicates magnitudes of electrochemical potential, or voltage. An irreversible phase transition peak occurs for LiCoO₂ at a potential of about 4.45 V. However, after substituting Co with Mn, the phase transition shifted to a potential of about 4.55V with reduced peak intensity. Such behavior indicates that substitutions for Co (e.g., Mn substituting for Co) can produce cathode active materials of high voltage stability.

FIG. 25 presents voltage profile curves for cathode active materials represented by compositions of Li_(1.05)Co_(0.96)Mn_(0.04)O₂, Li_(1.05)Co_(0.93)Mn_(0.07)O₂, Li_(1.110)Co_(0.90)Mn_(0.10)O₂, and Li_(1.19)Co_(0.72)Mn_(0.28)O₂. These cathode active materials were prepared according to the co-precipitation method described above and then packaged into 2032 coin half-cells. The voltage profile corresponds to a first charge-discharge cycle at a C/10 charge-discharge rate in the voltage window of 2.75-4.6V. In FIG. 25, the ordinate indicates magnitudes of electrochemical potential (i.e., V) for the coin half cells, and the abscissa indicates magnitudes of storage capacity (i.e., mAh/g). For all compositions, high specific capacities (i.e., >150 mAh/g) and high average voltages (i.e., >3.7V) are achieved. For cathode active materials of Li_(1.19)Co_(0.72)Mn_(0.28)O₂, a plateau at approximately 4.5V in the first charging curve indicates an activation process for a Li₂MnO₃-like phase present in the material.

Example 18—Tuning of Battery Performance

It will be appreciated that factors such as substitution for Co (e.g., Co_(1-x-y)M_(y)Mn_(x)) and ratios of lithium to Co and its substitutes (i.e., [Li]/[Co_(1-x-y)M_(y)Mn_(x)]) influence the phases present in cathode active materials. As evidenced by FIGS. 20-21 and 23, such factors may be selected to produce cathode active materials of single phase (e.g., R3m crystal structure). Moreover, as evidenced by FIGS. 24 and 25, such factors may also be selected to improve battery performance (e.g., increase voltage stability).

FIG. 26 presents a contour plot of discharge energy density that varies with substitution (i.e., Co_(1-x)Mn_(x)) and lithium ratio (i.e., [Li]/[Co_(1-x)Mn_(x)]). The discharge energy density corresponds to measurements from 2032 coin half-cells during at first cycle and taken at a charge-discharge rate of C/10. The contour plot was generated from a combination of sample measurements and predictive modeling. The 2032 coin half-cells used cathode active materials prepared according to the sol-gel method described above, where 0≦x≦0.28. In FIG. 26, two regions are present that indicate high energy density (i.e., >700 Wh/kg): [1] a first region for Mn content up to about 12% (i.e., x≦0.12.) and a ratio up to about 1.15 (i.e., [Li]/[Co_(1-x)Mn_(x)]≦1.15), and [2] a second region for Mn content higher than about 25% (i.e., x>0.25) and a ratio higher than about 1.25 (i.e., [Li]/[Co_(1-x)Mn_(x)]>1.25).

FIG. 27 presents a contour plot of energy retention that varies with substitution (i.e., Co_(1-x)Mn_(x)) and lithium ratio (i.e., [Li]i[Co_(1-x)Mn_(x)]). The energy retention corresponds to measurements from 2032. coin half-cells after 10 cycles and taken at a charge-discharge rate of C/3. The contour plot was generated from a combination of sample measurements and predictive modeling. The 2032 coin half-cells used cathode active materials prepared according to the sol-gel method described above, where 0≦x≦0.28. Similar to FIG. 26, two regions are present in FIG. 27 that indicate high energy density (i.e., >700): [1] a first region for Mn content up to about 12% (i.e., x≦0.12) and a ratio up to about 1.15 (i.e., [Li]/[Co_(1-x)Mn_(x)]≦1.15), and [2] a second region for Mn content higher than about 25% (i.e., x>0.25) and a ratio higher than about 1.25 (i.e., [Li]/[Co_(1-x)Mn_(x)]>1.25).

Example 19

Four samples of Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ) were made into coin cells with a Li metal anode and cycled from 2.75-4.5V at C/5 charge/discharge rate. The four samples corresponded to x=0.01, 0.02, 0.03, and 0.04 where α=1.0; y ranged from 0.001-0.003; and δ was about 2.0. FIGS. 28 & 29 show plots of the derivative of the differential capacity with respect to electrochemical potential (i.e., dQ/dV vs V) illustrating the effect of Mn and Li content on battery cell performance. During the charge and discharge of a LiCoO₂ cathode, a phase transition from the hexagonal to monoclinic phase takes place between 4.0-4.3V (see FIG. 29). The phase transition also occurs for Mn substitutions of x=0.01 (see FIG. 28). The phase transition results in a volume expansion of the crystal lattice that may contribute to capacity fade of the electrode. In such situations, the substitution of Mn for Co in proportions greater than x=0.01 mitigates this phase transition, as demonstrated in FIG. 28 for compositions of x=0.02, 0.03, and 0.04.

The phase transition is also dependent on the Li content in the compound. When considering Mn substitutions as in Li_(α)Co_(0.97)Mn_(0.03)O₂, the phase transition can be mitigated if α≧1.0. FIG. 29 illustrates that, as the Li content increases from 0.977 to 1.014, the characteristic phase transition peaks in the dQ/dV curve between 4.0-4.3V reduce to a flat line for α=1.014.

On the other hand, the benefit of Li excess is limited by its effect on volumetric energy density and retention. FIG. 30 demonstrates the effect. of Li content in Li_(α)Co_(0.97)Mn_(0.03)O₂ on the discharge energy during cycling between 2.75-4.5 V at a C/5 rate. The stoichiometric composition, α=1.003, shows a maximum energy of 754 Wh/g, and loses about 8% of that energy in 25 cycles. The Li rich sample (i.e., α=1.014) has a similar maximum but loses 10% of its energy. The sub-stoichiometric compositions (i.e., α≦1.0) compositions show lower energies. This behavior and repeated tests with 2% Mn (i.e., x=0.02) indicate that the best energy and energy retention is obtained at a lithium content where a is about 1.00. The compositional values for each metal in the materials were determined by high precision ICP-OES analysis, with special regard to the measurement of the lithium content (i.e., α).

Similar electrochemical measurements (not shown) also illustrate an effect of aluminum content on the mitigation of the hexagonal to monoclinic phase change. As aluminum is substituted into an otherwise fixed composition of Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ), the phase transformation is suppressed.

There may be a, x, and y where volumetric energy, energy retention and suppression of the phase transition occurs. From this examination it is determined that any substitution of Mn, Al, and Li, addition or other elements that can be substituted into the structure at total amounts of ≧3% (i.e., x≧0.03) will mitigate the hexagonal to monoclinic transition that occurs between 4.0-4.3V. It seems that the additions are also related to a sum of their oxidation states, i.e., Mn⁴⁺, Al³⁺, and Li⁺ should be added up to some level to prevent the phase transition. This is because it has been observed that different Li stoichiometries for a given Mn content are needed to prevent the phase transition.

Example 20

The optimum Mn content (i.e., x) to achieve the greatest volumetric energy density and energy retention of Mn-substituted LiCoO₂, cycling between 2.75-4.5 V at a C/5 rate is determined to lie between x=0.02 and x=0.04 as illustrated in FIG. 31. Battery cells including three compositions of x=0.02, 0.03, and 0.04 and containing similar Li and Al content were cycled from 2.75 to 4.5 V at a C/5 rate. The composition corresponding to x=0.03, although showing slightly lower initial energy compared to x=0.02, demonstrates the highest energy retention.

Example 21—Nuclear Magnetic Resonance

Solid-state ⁶Li nuclear magnetic resonance (NMR) measurements have identified Mn—Mn clustering in Li_(α)Co_(1-x)Mn_(x)O_(δ). Which clustering, would eventually lead to the formation of Li₂MnO₃ as Mn and Li content is increased beyond the phase limit for Li-rich compositions. Without wishing to be held to a particular mechanism or mode of action, Mn clustering stabilized the cathode structure, which can provide materials described herein with high voltage stability as shown in any electrochemical tests.

Though HR-XRD and NMR did not show any Li₂MnO₃ formation for the compositions considered in this work. New phases peaks correspond to Li₂MnO₃ are absent in both HR-XRD and NMR spectra. FIG. 32 shows a comparison of x=0.03 and x=0.04 for Mn-substituted LiCoO₂. Quantification of the NMR at the designated resonances show that the clustering of manganese for x=0.04 is double that for x=0.03, rather than the expected 25% increase. Although Mn substitution is considered to stabilize the LiCoO₂ R3m crystal structure, large Mn clusters tend to incorporate Li into the transition metal (TM) layer, so that when Li is extracted from the crystal structure at higher voltage (4.5V), if Li in the transition metal layer drops into the lithium layer, vacancies created in the transition metal layer are destabilizing to the crystal structure.

Example 22—Aluminum Addition

Three cathode active materials with the composition Li_(1.01)Co_(0.97-y)Al_(y)Mn_(0.03)O_(δ) were made, fixing the Li and Mn content to 1.01 and 0.03, respectively, while varying the Al content to 0.077, 0.159 and 0.760 wt. %. The cathode active materials were tested in haft-cells, cycling from 2.75-4.5V at a rate of C/5. FIG. 33 shows that as Al substitution is increased, the discharge energy decreases. However, the energy retention is improved with Al addition, with the largest substitution of 0.76 wt % Al exhibiting the best discharge energy after 25 cycles.

Example 23—Particle Morphology

To achieve stable and high energy densities, cathode active materials of composition of Li_(α)Co_(1-x-y)Al_(y)Mn_(x)O_(δ) can be processed at sufficient temperatures and times such that secondary particles contain dense single grains (i.e., primary particles). These dense single grains can impart high strength to withstand calendaring processes during electrode fabrication and battery cell assembly. FIGS. 34A-34B & 35A-35B illustrate the effect of optimum processing to achieve high strength particles.

When precursor powders are processed at sufficient temperature and time, the multigrain structure found in FIG. 34A can be further sintered to gain larger and stronger grains as in FIG. 34B that are more difficult to crush. This improved strength is demonstrated in FIGS. 35A-35B. The size distribution of the precursor powder calcined at 1050° C. (FIG. 35A) grows from 18 to 22 due to the partial interconnection due to sintering. When the powder is pressed into a pellet and the particles are crushed under pressure a simulation of electrode laminate calendering), the particle size distribution is reduced into a bimodal distribution due to the breaking of particle-particle bonds (i.e., between primary particles) and particle fracture into smaller primary grains. However, when the temperature at the same processing time is raised to 1085° C., large single grains, which have sintered together during processing, break down to the original precursor size, but no further. This strength prevents the formation of new surfaces, such as surfaces which are not protected with an Al₂O₃ coating, and are subject to interaction with the electrolyte.

Example 24—Energy Retention

The calcination temperature not only affects particle strength, but the energy retention of the cathode active material as an electrode. As the calcination temperature increases the energy retention also increases to a maximum between 1075-1080° C. (FIG. 36). The change in surface area after compacting powder calcined at increasing temperatures stabilizes as the particle strength increases and no new surfaces are exposed due to crushing particles. FIG. 36 shows the correlation between strength (stabilized surface area change) and energy retention of the cathode active material. In FIG. 36, the cathode active material has a composition where the lithium to transition metal ratio (Li/TM) is 1.01 (i.e., α=1.01 and y=0).

The discharge capacity and coulombic efficiency of first cycle of the cathode material is also correlated to the calcination temperature. FIG. 37 illustrates this relationship. The initial discharge capacity and effectively, the initial energy decreases as the calcination temperature of the material is increased from 1050-1092° C. The coulombic efficiency is a measure of the amount of Li intercalated hack into the cathode during the first discharge, showing the fraction of Li that is eliminated from future charge/discharge cycling. The maximum efficiency occurs at 1080° C., whereas the capacity while regarding the particle strength has an optimum 1070-1080° C. This sensitivity of the temperature of calcination is part of the novelty of the proposed invention, since it is shown to affect particle strength, energy retention, Li content, cyclability, capacity and energy of the material.

Example 25—Thermal Stability

Along with the high energy of Li-ion battery materials comes the increased risk of unplanned energy release, e.g., heat that can cause a battery cell to catch fire. Differential scanning calorimetry (DSC) of cathode active materials charged and exposed to electrolyte help determine the risk of thermal failure. FIG. 38 shows DSC measurements of five Mn-substituted LiCoO₂ compositions from Mn=1-7 mole % (i.e. x=0.01-0.07). Compared to commercial LCO (i.e., LiCoO₂), the Mn 1% composition (i.e., x=0.01) shows a lower onset temperature to an exothermal reaction evolving more heat. However, as Mn content increases, the onset temperature of the reaction increases and the total heat released is reduced up to Mn 7%. After Mn=4%, onset temperature increases, but the heat release of the reaction begins to increase again. TABLE 4 enumerates these values. Based on the DSC measurements, the optimum Mn substitution is between Mn 3-4 mole % (i.e., 0.03≦x≦0.04).

TABLE 4 Summary of DSC Measurements 1% Mn 2% Mn 3% Mn 4% Mn 7% Mn Sample Chemistry LiCoO₂ (x = 0.01) (x = 0.02) (x = 0.03) (x = 0.04) (x = 0.07) Average Onset Temperature 186° C. 177° C. 196° C. 243° C. 245° C. 250° C. Average Heat Released (50-400° C.) 0.52 J/g 0.57 J/g 0.38 J/g 0.16 J/g 0.15 J/g 0.3 J/g

Example 26—Lattice Parameters

The Li content (i.e., α), critical to the performance of the material, is associated with a change in the c-lattice parameter of the crystal structure varies as shown in FIG. 39. Depending on the Mn content, which also increases the c-lattice parameter as Mn is increased, the Li content will reduce the c-lattice value as Li increases. It also appears that capability of the materials to accommodate for excess lithium in the cathode active material while maintaining the R3m crystal structure increases with increasing Mn content. This phase diagram of the LiCo_((1-x))MnO₂ system provides a map of the optimum Li addition without forming secondary phases.

Example 27—Raman Spectra

The Raman spectra of the layered LiCoO₂ and Mn-substituted LiCoO₂ (i.e., x=0.04 and 0.07) are shown in FIG. 40. The Raman spectra were obtained using 785-nm photonic excitation. According to factor-group analysis, the layered LiCoO₂ with R3m crystal structure is predicted to show two Raman-active modes, i.e., one at ca. 596 cm⁻¹ with A1_(g) symmetry due to a symmetric oxygen vibration along the c-axis and one at ca. 486 cm⁻¹ with E_(g) symmetry due to two degenerate symmetric oxygen vibrations in the a/b crystallographic plane. With the addition of Mn into the structure, new Raman scattering features appear at frequencies above the 596 cm⁻¹ band and below the 486 cm⁻¹ band. This new scattering is due to Mn—O bond stretching vibrations associated with the various Mn—Co—Li occupancies that form throughout the transition metal layer. The relative intensity of the bands caused by these new Mn—O vibrations increases with increasing Mn substitution. The band near 320 cm⁻¹ is from the CaF₂ window through which the Raman spectra are taken.

Example 28—Stability to Oxidation

The oxidative stability results for 7% Mn substitution (i.e., x=0.07) compared with 4% Mn substitution (i.e., x=0.04) are shown in FIG. 41. Half-cells were charged from an open circuit value to 4.65V and then cycled between 4.0 V and 4.65 V in a continuous cycling run. The 52nd cycle was a full cycle taken between 2.75 to 4.65 V. In FIG. 41, the plot of discharge capacity at 52nd cycle versus lithium to transition metal ratio (i.e., α where y=0) shows that the optimum capacity occurs at Li content (α) near unity. Compared to x=0.04 under these cycling conditions, the x=0.07 substitution maintains a higher capacity over 52 cycles, which shows better capacity retention under these conditions.

In FIG. 42, the dQ/dV of a half-cell incorporating a cathode active material of Li_(1.00)Co_(0.93-y)Al_(y)Mn_(0.07)O_(δ) is plotted with the dQ/dV of a half-cell incorporating a cathode active material of Li_(1.025)Co_(0.96-y)Al_(y)Mn_(0.04)O_(δ). FIG. 42 shows that the reduction process for the x=0.07 sample at high voltage occurs at approximately 4.53V. However, another reduction peal: for the x=0.04 sample is evident at 4.47 V, which indicates possible instability or additional phase changes. Such instability or phases changes may lead to structural transformations with cycling. Note that there is no respective charge peak for this reduction process which could indicate irreversibility and thus inferior capacity retention when cycled to higher voltages of 4.65 V as discussed in FIG. 41.

Example 29—Capacity and Coulombic Efficiency

The capacity on the first cycle is depicted in FIG. 43 wherein the first cycle charge and discharge values are plotted as a function of the lithium to transition metal ratio (i.e., α where y=0) along with the calculated coulombic efficiencies. The improvement in coulombic efficiency is better for near stoichiometric values. The greater α the more Li can be extracted out of the cathode active material. However, and in converse, the higher the Li content, the lower the resultant discharge capacity. An optimal α is hence investigated.

Example 30—X-Ray Absorption

From X-ray absorption (XAS) results (not shown here), for all compounds throughout the series, Co is in the +3 oxidation state and Mn in the +4 oxidation state for all α values in the Mn-substituted LiCoO₂ samples. As such, the calculated stoichiometry is Li_(0.983)Co_(0.914)Mn_(0.069)O₂ and Li is deficient in the Li layer. Moving Li cations out from the Li layer to satisfy for transition metal layer leads to Li_(0.966)[Li_(0.017)Co_(0.914)Mn_(0.069)]O₂. (Note that the bracketed values for Li, Co, and Mn sum to unity.) For the purposes of this summary we further distinguish this material as having about 5% Li-deficiencies in the Li layer and some small amount of Li in the TM layer to join with Mn to make Mn—Li—Mn domains in place of Co—Co—Co domains with charge compensation being a key to the stability of the resulting lattice LiMn₂. However, the size of these units is limited as suggested by density functional theory (DFT) total energy calculations (not shown), and shows greater stability in the model as compared to x=0.04 under the above cycling conditions.

The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings. 

What is claimed is:
 1. A compound represented by Formula (I): Li_(α)Co_(1-x)Mn_(x)O_(δ)  (IV) wherein: 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20.
 2. The compound of claim 1, wherein 1.00≦α≦1.05.
 3. The compound of claim 1, wherein 1.01≦α≦1.05 and 0.02≦x≦0.05.
 4. The compound of claim 1, wherein 1.01≦α≦1.05 and x=0.04.
 5. The compound of claim 1, wherein the compound has a structure represented by Formula (Va) or Formula (Vb): (x)[Li₂MnO₃].(1-x)[LiCoO₂]  (Va) (x)[Li₂MnO₃].(1-x)[Li_((1-y))Co_((1-y))Mn_(y)O₂]  (Vb) wherein 0≦x≦0.10 and 0≦γ≦0.10.
 6. A powder comprising particles, the particles comprising a compound represented by Formula (IV): Li_(α)Co_(1-x)Mn_(x)O_(δ)  (IV) wherein 0.95≦α≦1.10, 0≦x≦0.10, and 1.90≦δ≦2.20.
 7. The powder of claim 6, wherein the compound has a structure represented by Formula (IIa): (x)[Li₂MnO₃].(1-x)[LiCoO₂]  (Va) (x)[Li₂MnO₃].(1-x)[Li_((1-y))Co_((1-y))Mn_(y)O₂]  (Vb) wherein 0≦x≦0.10 and 0≦γ≦0.10.
 8. The powder of claim 6, wherein at least a portion of the particles have a smooth surface.
 9. The powder of claim 6, wherein at least a portion of the particles have a tap density equal to or greater than 2.2 g/cm³.
 10. The powder of claim 6, wherein at least a portion of the particles have a smooth surface and a tap density equal to or greater than 2.2 g/cm³.
 11. The powder of claim 6, wherein 0.98≦α≦1.01, x=0.03.
 12. The powder of claim 6, wherein 1.01≦α≦1.05 and 0.02≦x≦0.05.
 13. The powder of claim 6, wherein 1.01≦α≦1.05 and x=0.04.
 14. A cathode active material comprising the compound of claim
 1. 15. A cathode active material comprising the powder of claim
 6. 16. A cathode comprising a cathode active material of claim
 14. 17. A battery cell, comprising: an anode, comprising an anode current collector, and an anode active material disposed over the anode current collector; the cathode according to claim 16; and a separator disposed between the anode and the cathode.
 18. A portable electronic device, comprising: a set of components powered by a battery pack, the battery pack comprising the battery cell according to claim
 17. 19. A method for producing a powder comprising the compound of claim 1, comprising: mixing a lithium source with precursor particles to produce a reactant, the precursor particles comprising a transition-metal hydroxide comprising Co and Mn; and heating the reactant to a temperature equal to or greater than 800° C.
 20. The method of claim 19, wherein the temperature is between 800-1200° C. 